diff --git a/includes/admin/list-tables/class-wc-admin-list-table-orders.php b/includes/admin/list-tables/class-wc-admin-list-table-orders.php
index 1b562292c2a..f9babc8825b 100644
--- a/includes/admin/list-tables/class-wc-admin-list-table-orders.php
+++ b/includes/admin/list-tables/class-wc-admin-list-table-orders.php
@@ -772,15 +772,22 @@ class WC_Admin_List_Table_Orders extends WC_Admin_List_Table {
 
 		// Filter the orders by the posted customer.
 		if ( ! empty( $_GET['_customer_user'] ) ) { // WPCS: input var ok.
-			// @codingStandardsIgnoreStart
-			$query_vars['meta_query'] = array(
-				array(
-					'key'   => '_customer_user',
-					'value' => (int) $_GET['_customer_user'], // WPCS: input var ok, sanitization ok.
-					'compare' => '=',
-				),
-			);
-			// @codingStandardsIgnoreEnd
+			$customer_id = (int) $_GET['_customer_user'];  // WPCS: input var ok, sanitization ok.
+
+			// On WC 3.5.0 the ID of the user that placed the order was moved from the post meta _customer_user to the post_author field in the wp_posts table.
+			if ( version_compare( get_option( 'woocommerce_db_version' ), '3.5.0', '>=' ) ) {
+				$query_vars['author'] = $customer_id;
+			} else {
+				// @codingStandardsIgnoreStart
+				$query_vars['meta_query'] = array(
+					array(
+						'key'     => '_customer_user',
+						'value'   => $customer_id,
+						'compare' => '=',
+					),
+				);
+				// @codingStandardsIgnoreEnd
+			}
 		}
 
 		// Sorting.
diff --git a/includes/admin/reports/class-wc-report-customers.php b/includes/admin/reports/class-wc-report-customers.php
index 503f470992f..326ad5334f5 100644
--- a/includes/admin/reports/class-wc-report-customers.php
+++ b/includes/admin/reports/class-wc-report-customers.php
@@ -69,46 +69,56 @@ class WC_Report_Customers extends WC_Admin_Report {
 	 * Output customers vs guests chart.
 	 */
 	public function customers_vs_guests() {
-
-		$customer_order_totals = $this->get_order_report_data(
-			array(
-				'data'         => array(
-					'ID' => array(
-						'type'     => 'post_data',
-						'function' => 'COUNT',
-						'name'     => 'total_orders',
-					),
+		$customer_args = array(
+			'data'         => array(
+				'ID' => array(
+					'type'     => 'post_data',
+					'function' => 'COUNT',
+					'name'     => 'total_orders',
 				),
-				'where_meta'   => array(
-					array(
-						'meta_key'   => '_customer_user',
-						'meta_value' => '0',
-						'operator'   => '>',
-					),
-				),
-				'filter_range' => true,
-			)
+			),
+			'filter_range' => true,
 		);
+		$guest_args    = $customer_args;
 
-		$guest_order_totals = $this->get_order_report_data(
-			array(
-				'data'         => array(
-					'ID' => array(
-						'type'     => 'post_data',
-						'function' => 'COUNT',
-						'name'     => 'total_orders',
-					),
+		// On WC 3.5.0 the ID of the user that placed the order was moved from the post meta _customer_user to the post_author field in the wp_posts table.
+		if ( version_compare( get_option( 'woocommerce_db_version' ), '3.5.0', '>=' ) ) {
+			$customer_args['where'] = array(
+				array(
+					'key'      => 'post_author',
+					'value'    => '0',
+					'operator' => '>',
 				),
-				'where_meta'   => array(
-					array(
-						'meta_key'   => '_customer_user',
-						'meta_value' => '0',
-						'operator'   => '=',
-					),
+			);
+
+			$guest_args['where'] = array(
+				array(
+					'key'      => 'post_author',
+					'value'    => '0',
+					'operator' => '=',
 				),
-				'filter_range' => true,
-			)
-		);
+			);
+		} else {
+			$customer_args['where_meta'] = array(
+				array(
+					'meta_key'   => '_customer_user',
+					'meta_value' => '0',
+					'operator'   => '>',
+				),
+			);
+
+			$guest_args['where_meta'] = array(
+				array(
+					'meta_key'   => '_customer_user',
+					'meta_value' => '0',
+					'operator'   => '=',
+				),
+			);
+		}
+
+		$customer_order_totals = $this->get_order_report_data( $customer_args );
+		$guest_order_totals = $this->get_order_report_data( $guest_args );
+
 		?>
 		<div class="chart-container">
 			<div class="chart-placeholder customers_vs_guests pie-chart" style="height:200px"></div>
@@ -246,61 +256,63 @@ class WC_Report_Customers extends WC_Admin_Report {
 	public function get_main_chart() {
 		global $wp_locale;
 
-		$customer_orders = $this->get_order_report_data(
-			array(
-				'data'         => array(
-					'ID'        => array(
-						'type'     => 'post_data',
-						'function' => 'COUNT',
-						'name'     => 'total_orders',
-					),
-					'post_date' => array(
-						'type'     => 'post_data',
-						'function' => '',
-						'name'     => 'post_date',
-					),
+		$customer_args = array(
+			'data'         => array(
+				'ID'        => array(
+					'type'     => 'post_data',
+					'function' => 'COUNT',
+					'name'     => 'total_orders',
 				),
-				'where_meta'   => array(
-					array(
-						'meta_key'   => '_customer_user',
-						'meta_value' => '0',
-						'operator'   => '>',
-					),
+				'post_date' => array(
+					'type'     => 'post_data',
+					'function' => '',
+					'name'     => 'post_date',
 				),
-				'group_by'     => $this->group_by_query,
-				'order_by'     => 'post_date ASC',
-				'query_type'   => 'get_results',
-				'filter_range' => true,
-			)
+			),
+			'group_by'     => $this->group_by_query,
+			'order_by'     => 'post_date ASC',
+			'query_type'   => 'get_results',
+			'filter_range' => true,
 		);
+		$guest_args    = $customer_args;
 
-		$guest_orders = $this->get_order_report_data(
-			array(
-				'data'         => array(
-					'ID'        => array(
-						'type'     => 'post_data',
-						'function' => 'COUNT',
-						'name'     => 'total_orders',
-					),
-					'post_date' => array(
-						'type'     => 'post_data',
-						'function' => '',
-						'name'     => 'post_date',
-					),
+		// On WC 3.5.0 the ID of the user that placed the order was moved from the post meta _customer_user to the post_author field in the wp_posts table.
+		if ( version_compare( get_option( 'woocommerce_db_version' ), '3.5.0', '>=' ) ) {
+			$customer_args['where'] = array(
+				array(
+					'key'      => 'post_author',
+					'value'    => '0',
+					'operator' => '>',
 				),
-				'where_meta'   => array(
-					array(
-						'meta_key'   => '_customer_user',
-						'meta_value' => '0',
-						'operator'   => '=',
-					),
+			);
+
+			$guest_args['where'] = array(
+				array(
+					'key'      => 'post_author',
+					'value'    => '0',
+					'operator' => '=',
 				),
-				'group_by'     => $this->group_by_query,
-				'order_by'     => 'post_date ASC',
-				'query_type'   => 'get_results',
-				'filter_range' => true,
-			)
-		);
+			);
+		} else {
+			$customer_args['where_meta'] = array(
+				array(
+					'meta_key'   => '_customer_user',
+					'meta_value' => '0',
+					'operator'   => '>',
+				),
+			);
+
+			$guest_args['where_meta'] = array(
+				array(
+					'meta_key'   => '_customer_user',
+					'meta_value' => '0',
+					'operator'   => '=',
+				),
+			);
+		}
+
+		$customer_orders = $this->get_order_report_data( $customer_args );
+		$guest_orders = $this->get_order_report_data( $guest_args );
 
 		$signups         = $this->prepare_chart_data( $this->customers, 'user_registered', '', $this->chart_interval, $this->start_date, $this->chart_groupby );
 		$customer_orders = $this->prepare_chart_data( $customer_orders, 'post_date', 'total_orders', $this->chart_interval, $this->start_date, $this->chart_groupby );
diff --git a/includes/api/class-wc-rest-orders-controller.php b/includes/api/class-wc-rest-orders-controller.php
index 02957242ac0..c9121bb4465 100644
--- a/includes/api/class-wc-rest-orders-controller.php
+++ b/includes/api/class-wc-rest-orders-controller.php
@@ -365,15 +365,20 @@ class WC_REST_Orders_Controller extends WC_REST_Legacy_Orders_Controller {
 		}
 
 		if ( isset( $request['customer'] ) ) {
-			if ( ! empty( $args['meta_query'] ) ) {
-				$args['meta_query'] = array(); // WPCS: slow query ok.
-			}
+			// On WC 3.5.0 the ID of the user that placed the order was moved from the post meta _customer_user to the post_author field in the wp_posts table.
+			if ( version_compare( get_option( 'woocommerce_db_version' ), '3.5.0', '>=' ) ) {
+				$args['author'] = $request['customer'];
+			} else {
+				if ( ! empty( $args['meta_query'] ) ) {
+					$args['meta_query'] = array(); // WPCS: slow query ok.
+				}
 
-			$args['meta_query'][] = array(
-				'key'   => '_customer_user',
-				'value' => $request['customer'],
-				'type'  => 'NUMERIC',
-			);
+				$args['meta_query'][] = array(
+					'key'   => '_customer_user',
+					'value' => $request['customer'],
+					'type'  => 'NUMERIC',
+				);
+			}
 		}
 
 		// Search by product.
diff --git a/includes/api/v1/class-wc-rest-orders-controller.php b/includes/api/v1/class-wc-rest-orders-controller.php
index 804e3fb571e..f617192c0bb 100644
--- a/includes/api/v1/class-wc-rest-orders-controller.php
+++ b/includes/api/v1/class-wc-rest-orders-controller.php
@@ -404,15 +404,20 @@ class WC_REST_Orders_V1_Controller extends WC_REST_Posts_Controller {
 		}
 
 		if ( isset( $request['customer'] ) ) {
-			if ( ! empty( $args['meta_query'] ) ) {
-				$args['meta_query'] = array();
-			}
+			// On WC 3.5.0 the ID of the user that placed the order was moved from the post meta _customer_user to the post_author field in the wp_posts table.
+			if ( version_compare( get_option( 'woocommerce_db_version' ), '3.5.0', '>=' ) ) {
+				$args['author'] = $request['customer'];
+			} else {
+				if ( ! empty( $args['meta_query'] ) ) {
+					$args['meta_query'] = array(); // WPCS: slow query ok.
+				}
 
-			$args['meta_query'][] = array(
-				'key'   => '_customer_user',
-				'value' => $request['customer'],
-				'type'  => 'NUMERIC',
-			);
+				$args['meta_query'][] = array(
+					'key'   => '_customer_user',
+					'value' => $request['customer'],
+					'type'  => 'NUMERIC',
+				);
+			}
 		}
 
 		// Search by product.
diff --git a/includes/class-wc-background-updater.php b/includes/class-wc-background-updater.php
index 3f80666a767..1c28f7f26da 100644
--- a/includes/class-wc-background-updater.php
+++ b/includes/class-wc-background-updater.php
@@ -132,4 +132,13 @@ class WC_Background_Updater extends WC_Background_Process {
 		WC_Install::update_db_version();
 		parent::complete();
 	}
+
+	/**
+	 * See if the batch limit has been exceeded.
+	 *
+	 * @return bool
+	 */
+	public function is_memory_exceeded() {
+		return $this->memory_exceeded();
+	}
 }
diff --git a/includes/class-wc-cart-totals.php b/includes/class-wc-cart-totals.php
index bb2c384a113..538977363f0 100644
--- a/includes/class-wc-cart-totals.php
+++ b/includes/class-wc-cart-totals.php
@@ -637,7 +637,7 @@ final class WC_Cart_Totals {
 			}
 
 			if ( $this->calculate_tax && $item->product->is_taxable() ) {
-				$total_taxes     = WC_Tax::calc_tax( $item->total, $item->tax_rates, $item->price_includes_tax );
+				$total_taxes     = apply_filters( 'woocommerce_calculate_item_totals_taxes', WC_Tax::calc_tax( $item->total, $item->tax_rates, $item->price_includes_tax ), $item, $this );
 				$item->taxes     = $total_taxes;
 				$item->total_tax = array_sum( array_map( array( $this, 'round_line_tax' ), $item->taxes ) );
 
diff --git a/includes/class-wc-cart.php b/includes/class-wc-cart.php
index d5ea1c5eb9a..293dcf772ec 100644
--- a/includes/class-wc-cart.php
+++ b/includes/class-wc-cart.php
@@ -1385,28 +1385,27 @@ class WC_Cart extends WC_Legacy_Cart {
 	 * @return string price or string for the shipping total
 	 */
 	public function get_cart_shipping_total() {
+
+		// Default total assumes Free shipping.
+		$total = __( 'Free!', 'woocommerce' );
+
 		if ( 0 < $this->get_shipping_total() ) {
 
 			if ( $this->display_prices_including_tax() ) {
-				$return = wc_price( $this->shipping_total + $this->shipping_tax_total );
+				$total = wc_price( $this->shipping_total + $this->shipping_tax_total );
 
 				if ( $this->shipping_tax_total > 0 && ! wc_prices_include_tax() ) {
-					$return .= ' <small class="tax_label">' . WC()->countries->inc_tax_or_vat() . '</small>';
+					$total .= ' <small class="tax_label">' . WC()->countries->inc_tax_or_vat() . '</small>';
 				}
-
-				return $return;
 			} else {
-				$return = wc_price( $this->shipping_total );
+				$total = wc_price( $this->shipping_total );
 
 				if ( $this->shipping_tax_total > 0 && wc_prices_include_tax() ) {
-					$return .= ' <small class="tax_label">' . WC()->countries->ex_tax_or_vat() . '</small>';
+					$total .= ' <small class="tax_label">' . WC()->countries->ex_tax_or_vat() . '</small>';
 				}
-
-				return $return;
 			}
-		} else {
-			return __( 'Free!', 'woocommerce' );
 		}
+		return apply_filters( 'woocommerce_cart_shipping_total', $total, $this );
 	}
 
 	/**
diff --git a/includes/class-wc-emails.php b/includes/class-wc-emails.php
index 207b00c1d84..1ff431bc6c5 100644
--- a/includes/class-wc-emails.php
+++ b/includes/class-wc-emails.php
@@ -223,11 +223,6 @@ class WC_Emails {
 		$this->emails['WC_Email_Customer_New_Account']      = include 'emails/class-wc-email-customer-new-account.php';
 
 		$this->emails = apply_filters( 'woocommerce_email_classes', $this->emails );
-
-		// include css inliner.
-		if ( ! class_exists( 'Emogrifier' ) && class_exists( 'DOMDocument' ) ) {
-			include_once dirname( __FILE__ ) . '/libraries/class-emogrifier.php';
-		}
 	}
 
 	/**
diff --git a/includes/class-wc-geolite-integration.php b/includes/class-wc-geolite-integration.php
index 2d97ccd54f8..49e9fc9941f 100644
--- a/includes/class-wc-geolite-integration.php
+++ b/includes/class-wc-geolite-integration.php
@@ -46,7 +46,7 @@ class WC_Geolite_Integration {
 
 	/**
 	 * Get country 2-letters ISO by IP address.
-	 * Retuns empty string when not able to find any ISO code.
+	 * Returns empty string when not able to find any ISO code.
 	 *
 	 * @param string $ip_address User IP address.
 	 * @return string
@@ -55,9 +55,12 @@ class WC_Geolite_Integration {
 		$iso_code = '';
 
 		try {
-			$reader   = new MaxMind\Db\Reader( $this->database ); // phpcs:ignore PHPCompatibility.PHP.NewLanguageConstructs.t_ns_separatorFound
-			$data     = $reader->get( $ip_address );
-			$iso_code = $data['country']['iso_code'];
+			$reader = new MaxMind\Db\Reader( $this->database ); // phpcs:ignore PHPCompatibility.PHP.NewLanguageConstructs.t_ns_separatorFound
+			$data   = $reader->get( $ip_address );
+
+			if ( isset( $data['country']['iso_code'] ) ) {
+				$iso_code = $data['country']['iso_code'];
+			}
 
 			$reader->close();
 		} catch ( Exception $e ) {
diff --git a/includes/class-wc-install.php b/includes/class-wc-install.php
index b0bcb358020..e07100c8262 100644
--- a/includes/class-wc-install.php
+++ b/includes/class-wc-install.php
@@ -109,6 +109,10 @@ class WC_Install {
 			'wc_update_343_cleanup_foreign_keys',
 			'wc_update_343_db_version',
 		),
+		'3.5.0' => array(
+			'wc_update_350_order_customer_id',
+			'wc_update_350_db_version',
+		),
 	);
 
 	/**
diff --git a/includes/class-wc-regenerate-images.php b/includes/class-wc-regenerate-images.php
index ae9c371f3dd..c3cb3352817 100644
--- a/includes/class-wc-regenerate-images.php
+++ b/includes/class-wc-regenerate-images.php
@@ -36,11 +36,7 @@ class WC_Regenerate_Images {
 	public static function init() {
 		add_action( 'image_get_intermediate_size', array( __CLASS__, 'filter_image_get_intermediate_size' ), 10, 3 );
 		add_filter( 'wp_generate_attachment_metadata', array( __CLASS__, 'add_uncropped_metadata' ) );
-
-		// Resize WooCommerce images on the fly when browsing site through customizer as to showcase image setting changes in real time.
-		if ( is_customize_preview() ) {
-			add_filter( 'wp_get_attachment_image_src', array( __CLASS__, 'maybe_resize_image' ), 10, 4 );
-		}
+		add_filter( 'wp_get_attachment_image_src', array( __CLASS__, 'maybe_resize_image' ), 10, 4 );
 
 		// Not required when Jetpack Photon is in use.
 		if ( method_exists( 'Jetpack', 'is_module_active' ) && Jetpack::is_module_active( 'photon' ) ) {
@@ -206,18 +202,32 @@ class WC_Regenerate_Images {
 		}
 
 		// Use a whitelist of sizes we want to resize. Ignore others.
-		if ( ! in_array( $size, apply_filters( 'woocommerce_image_sizes_to_resize', array( 'woocommerce_thumbnail', 'woocommerce_gallery_thumbnail', 'woocommerce_single', 'shop_thumbnail', 'shop_catalog', 'shop_single' ) ), true ) ) {
+		if ( ! $image || ! in_array( $size, apply_filters( 'woocommerce_image_sizes_to_resize', array( 'woocommerce_thumbnail', 'woocommerce_gallery_thumbnail', 'woocommerce_single', 'shop_thumbnail', 'shop_catalog', 'shop_single' ) ), true ) ) {
 			return $image;
 		}
 
-		// Get image metadata - we need it to proceed.
-		$imagemeta = wp_get_attachment_metadata( $attachment_id );
+		$image_size  = wc_get_image_size( $size );
+		$ratio_match = false;
 
-		if ( empty( $imagemeta ) ) {
-			return $image;
+		// If '' is passed to either size, we test ratios against the original file. It's uncropped.
+		if ( '' === $image_size['width'] || '' === $image_size['height'] ) {
+			$imagedata = wp_get_attachment_metadata( $attachment_id );
+
+			if ( ! $imagedata ) {
+				return $image;
+			}
+
+			if ( ! isset( $imagedata['file'] ) && isset( $imagedata['sizes']['full'] ) ) {
+				$imagedata['height'] = $imagedata['sizes']['full']['height'];
+				$imagedata['width']  = $imagedata['sizes']['full']['width'];
+			}
+
+			$ratio_match = wp_image_matches_ratio( $image[1], $image[2], $imagedata['width'], $imagedata['height'] );
+		} else {
+			$ratio_match = wp_image_matches_ratio( $image[1], $image[2], $image_size['width'], $image_size['height'] );
 		}
 
-		if ( ! isset( $imagemeta['sizes'], $imagemeta['sizes'][ $size ] ) || ! self::image_size_matches_settings( $imagemeta['sizes'][ $size ], $size ) ) {
+		if ( ! $ratio_match ) {
 			return self::resize_and_return_image( $attachment_id, $image, $size, $icon );
 		}
 
@@ -316,28 +326,30 @@ class WC_Regenerate_Images {
 			include ABSPATH . 'wp-admin/includes/image.php';
 		}
 
-		$thumbnail = self::get_image( $fullsizepath, $image_size['width'], $image_size['height'], $image_size['crop'] );
+		self::$regenerate_size = is_customize_preview() ? $size . '_preview' : $size;
 
-		// If the file is already there perhaps just load it.
-		if ( $thumbnail && file_exists( $thumbnail['filename'] ) ) {
-			$wp_uploads     = wp_upload_dir( null, false );
-			$wp_uploads_dir = $wp_uploads['basedir'];
-			$wp_uploads_url = $wp_uploads['baseurl'];
+		if ( is_customize_preview() ) {
+			// Make sure registered image size matches the size we're requesting.
+			add_image_size( self::$regenerate_size, absint( $image_size['width'] ), absint( $image_size['height'] ), $image_size['crop'] );
 
-			return array(
-				0 => str_replace( $wp_uploads_dir, $wp_uploads_url, $thumbnail['filename'] ),
-				1 => $thumbnail['width'],
-				2 => $thumbnail['height'],
-			);
+			$thumbnail = self::get_image( $fullsizepath, absint( $image_size['width'] ), absint( $image_size['height'] ), $image_size['crop'] );
+
+			// If the file is already there perhaps just load it if we're using the customizer. No need to store in meta data.
+			if ( $thumbnail && file_exists( $thumbnail['filename'] ) ) {
+				$wp_uploads     = wp_upload_dir( null, false );
+				$wp_uploads_dir = $wp_uploads['basedir'];
+				$wp_uploads_url = $wp_uploads['baseurl'];
+
+				return array(
+					0 => str_replace( $wp_uploads_dir, $wp_uploads_url, $thumbnail['filename'] ),
+					1 => $thumbnail['width'],
+					2 => $thumbnail['height'],
+				);
+			}
 		}
 
 		$metadata = wp_get_attachment_metadata( $attachment_id );
 
-		// Make sure registered image size matches the size we're requesting.
-		add_image_size( $size . '_preview', $image_size['width'], $image_size['height'], $image_size['crop'] );
-
-		self::$regenerate_size = $size . '_preview';
-
 		// We only want to regen a specific image size.
 		add_filter( 'intermediate_image_sizes', array( __CLASS__, 'adjust_intermediate_image_sizes' ) );
 
@@ -352,14 +364,13 @@ class WC_Regenerate_Images {
 			return $image;
 		}
 
-		// Since this is only a preview we should not update the actual size. That will be done later by the background job.
-		if ( isset( $new_metadata['sizes'][ $size . '_preview' ] ) ) {
-			$metadata['sizes'][ $size . '_preview' ] = $new_metadata['sizes'][ $size . '_preview' ];
+		if ( isset( $new_metadata['sizes'][ self::$regenerate_size ] ) ) {
+			$metadata['sizes'][ self::$regenerate_size ] = $new_metadata['sizes'][ self::$regenerate_size ];
 			wp_update_attachment_metadata( $attachment_id, $metadata );
 		}
 
 		// Now we've done our regen, attempt to return the new size.
-		$new_image = image_downsize( $attachment_id, $size . '_preview' );
+		$new_image = image_downsize( $attachment_id, self::$regenerate_size );
 
 		return $new_image ? $new_image : $image;
 	}
diff --git a/includes/class-woocommerce.php b/includes/class-woocommerce.php
index a98d4076c85..9f7e1380f85 100644
--- a/includes/class-woocommerce.php
+++ b/includes/class-woocommerce.php
@@ -20,7 +20,7 @@ final class WooCommerce {
 	 *
 	 * @var string
 	 */
-	public $version = '3.4.0';
+	public $version = '3.5.0';
 
 	/**
 	 * The single instance of the class.
diff --git a/includes/data-stores/abstract-wc-order-data-store-cpt.php b/includes/data-stores/abstract-wc-order-data-store-cpt.php
index 73ff2844cb0..0d6208887da 100644
--- a/includes/data-stores/abstract-wc-order-data-store-cpt.php
+++ b/includes/data-stores/abstract-wc-order-data-store-cpt.php
@@ -67,7 +67,7 @@ abstract class Abstract_WC_Order_Data_Store_CPT extends WC_Data_Store_WP impleme
 					'post_type'     => $order->get_type( 'edit' ),
 					'post_status'   => 'wc-' . ( $order->get_status( 'edit' ) ? $order->get_status( 'edit' ) : apply_filters( 'woocommerce_default_order_status', 'pending' ) ),
 					'ping_status'   => 'closed',
-					'post_author'   => 1,
+					'post_author'   => is_callable( array( $order, 'get_customer_id' ) ) ? $order->get_customer_id() : 0,
 					'post_title'    => $this->get_post_title(),
 					'post_password' => uniqid( 'order_' ),
 					'post_parent'   => $order->get_parent_id( 'edit' ),
@@ -139,7 +139,7 @@ abstract class Abstract_WC_Order_Data_Store_CPT extends WC_Data_Store_WP impleme
 		$changes = $order->get_changes();
 
 		// Only update the post when the post data changes.
-		if ( array_intersect( array( 'date_created', 'date_modified', 'status', 'parent_id', 'post_excerpt' ), array_keys( $changes ) ) ) {
+		if ( array_intersect( array( 'date_created', 'date_modified', 'status', 'parent_id', 'post_excerpt', 'customer_id' ), array_keys( $changes ) ) ) {
 			$post_data = array(
 				'post_date'         => gmdate( 'Y-m-d H:i:s', $order->get_date_created( 'edit' )->getOffsetTimestamp() ),
 				'post_date_gmt'     => gmdate( 'Y-m-d H:i:s', $order->get_date_created( 'edit' )->getTimestamp() ),
@@ -148,6 +148,7 @@ abstract class Abstract_WC_Order_Data_Store_CPT extends WC_Data_Store_WP impleme
 				'post_excerpt'      => $this->get_post_excerpt( $order ),
 				'post_modified'     => isset( $changes['date_modified'] ) ? gmdate( 'Y-m-d H:i:s', $order->get_date_modified( 'edit' )->getOffsetTimestamp() ) : current_time( 'mysql' ),
 				'post_modified_gmt' => isset( $changes['date_modified'] ) ? gmdate( 'Y-m-d H:i:s', $order->get_date_modified( 'edit' )->getTimestamp() ) : current_time( 'mysql', 1 ),
+				'post_author'       => is_callable( array( $order, 'get_customer_id' ) ) ? $order->get_customer_id() : 0,
 			);
 
 			/**
@@ -165,12 +166,27 @@ abstract class Abstract_WC_Order_Data_Store_CPT extends WC_Data_Store_WP impleme
 				wp_update_post( array_merge( array( 'ID' => $order->get_id() ), $post_data ) );
 			}
 			$order->read_meta_data( true ); // Refresh internal meta data, in case things were hooked into `save_post` or another WP hook.
+
+			// If customer changed, update any downloadable permissions.
+			if ( in_array( 'customer_id', $changes ) ) {
+				$this->update_downloadable_permissions( $order );
+			}
 		}
 		$this->update_post_meta( $order );
 		$order->apply_changes();
 		$this->clear_caches( $order );
 	}
 
+	/**
+	 * Update downloadable permissions for a given order.
+	 *
+	 * @param WC_Order $order Order object.
+	 */
+	protected function update_downloadable_permissions( $order ) {
+		$data_store = WC_Data_Store::load( 'customer-download' );
+		$data_store->update_user_by_order_id( $order->get_id(), $order->get_customer_id(), $order->get_billing_email() );
+	}
+
 	/**
 	 * Method to delete an order from the database.
 	 *
diff --git a/includes/data-stores/class-wc-customer-data-store.php b/includes/data-stores/class-wc-customer-data-store.php
index d907e61893c..8ad38340b3f 100644
--- a/includes/data-stores/class-wc-customer-data-store.php
+++ b/includes/data-stores/class-wc-customer-data-store.php
@@ -325,18 +325,27 @@ class WC_Customer_Data_Store extends WC_Data_Store_WP implements WC_Customer_Dat
 	public function get_last_order( &$customer ) {
 		global $wpdb;
 
-		$last_order = $wpdb->get_var(
-			// phpcs:disable WordPress.WP.PreparedSQL.NotPrepared
-			"SELECT posts.ID
+		// On WC 3.5.0 the ID of the user that placed the order was moved from the post meta _customer_user to the post_author field in the wp_posts table.
+		if ( version_compare( get_option( 'woocommerce_db_version' ), '3.5.0', '>=' ) ) {
+			$query = "SELECT ID
+			FROM $wpdb->posts
+			WHERE post_author = '" . esc_sql( $customer->get_id() ) . "'
+			AND   post_type = 'shop_order'
+			AND   post_status IN ( '" . implode( "','", array_map( 'esc_sql', array_keys( wc_get_order_statuses() ) ) ) . "' )
+			ORDER BY ID DESC";
+		} else {
+			$query = "SELECT posts.ID
 			FROM $wpdb->posts AS posts
 			LEFT JOIN {$wpdb->postmeta} AS meta on posts.ID = meta.post_id
 			WHERE meta.meta_key = '_customer_user'
 			AND   meta.meta_value = '" . esc_sql( $customer->get_id() ) . "'
 			AND   posts.post_type = 'shop_order'
 			AND   posts.post_status IN ( '" . implode( "','", array_map( 'esc_sql', array_keys( wc_get_order_statuses() ) ) ) . "' )
-			ORDER BY posts.ID DESC"
-			// phpcs:enable
-		);
+			ORDER BY posts.ID DESC";
+		}
+
+		// phpcs:ignore WordPress.WP.PreparedSQL.NotPrepared
+		$last_order = $wpdb->get_var( $query );
 
 		if ( ! $last_order ) {
 			return false;
@@ -358,17 +367,25 @@ class WC_Customer_Data_Store extends WC_Data_Store_WP implements WC_Customer_Dat
 		if ( '' === $count ) {
 			global $wpdb;
 
-			$count = $wpdb->get_var(
-				// phpcs:disable WordPress.WP.PreparedSQL.NotPrepared
-				"SELECT COUNT(*)
+			// On WC 3.5.0 the ID of the user that placed the order was moved from the post meta _customer_user to the post_author field in the wp_posts table.
+			if ( version_compare( get_option( 'woocommerce_db_version' ), '3.5.0', '>=' ) ) {
+				$query = "SELECT COUNT(*)
+				FROM $wpdb->posts
+				WHERE   post_type = 'shop_order'
+				AND     post_status IN ( '" . implode( "','", array_map( 'esc_sql', array_keys( wc_get_order_statuses() ) ) ) . "' )
+				AND     post_author = " . esc_sql( $customer->get_id() );
+			} else {
+				$query = "SELECT COUNT(*)
 				FROM $wpdb->posts as posts
 				LEFT JOIN {$wpdb->postmeta} AS meta ON posts.ID = meta.post_id
 				WHERE   meta.meta_key = '_customer_user'
 				AND     posts.post_type = 'shop_order'
 				AND     posts.post_status IN ( '" . implode( "','", array_map( 'esc_sql', array_keys( wc_get_order_statuses() ) ) ) . "' )
-				AND     meta_value = '" . esc_sql( $customer->get_id() ) . "'"
-				// phpcs:enable
-			);
+				AND     meta_value = '" . esc_sql( $customer->get_id() ) . "'";
+			}
+
+			// phpcs:ignore WordPress.WP.PreparedSQL.NotPrepared
+			$count = $wpdb->get_var( $query );
 			update_user_meta( $customer->get_id(), '_order_count', $count );
 		}
 
@@ -393,11 +410,18 @@ class WC_Customer_Data_Store extends WC_Data_Store_WP implements WC_Customer_Dat
 			global $wpdb;
 
 			$statuses = array_map( 'esc_sql', wc_get_is_paid_statuses() );
-			$spent    = $wpdb->get_var(
-				// phpcs:disable WordPress.WP.PreparedSQL.NotPrepared
-				apply_filters(
-					'woocommerce_customer_get_total_spent_query',
-					"SELECT SUM(meta2.meta_value)
+
+			// On WC 3.5.0 the ID of the user that placed the order was moved from the post meta _customer_user to the post_author field in the wp_posts table.
+			if ( version_compare( get_option( 'woocommerce_db_version' ), '3.5.0', '>=' ) ) {
+				$query = "SELECT SUM(meta.meta_value)
+					FROM $wpdb->posts as posts
+					LEFT JOIN {$wpdb->postmeta} AS meta ON posts.ID = meta.post_id
+					WHERE   posts.post_author   = '" . esc_sql( $customer->get_id() ) . "'
+					AND     posts.post_type     = 'shop_order'
+					AND     posts.post_status   IN ( 'wc-" . implode( "','wc-", $statuses ) . "' )
+					AND     meta.meta_key      = '_order_total'";
+			} else {
+				$query = "SELECT SUM(meta2.meta_value)
 					FROM $wpdb->posts as posts
 					LEFT JOIN {$wpdb->postmeta} AS meta ON posts.ID = meta.post_id
 					LEFT JOIN {$wpdb->postmeta} AS meta2 ON posts.ID = meta2.post_id
@@ -405,11 +429,11 @@ class WC_Customer_Data_Store extends WC_Data_Store_WP implements WC_Customer_Dat
 					AND     meta.meta_value     = '" . esc_sql( $customer->get_id() ) . "'
 					AND     posts.post_type     = 'shop_order'
 					AND     posts.post_status   IN ( 'wc-" . implode( "','wc-", $statuses ) . "' )
-					AND     meta2.meta_key      = '_order_total'",
-					$customer
-				)
-				// phpcs:enable
-			);
+					AND     meta2.meta_key      = '_order_total'";
+			}
+
+			// phpcs:ignore WordPress.WP.PreparedSQL.NotPrepared
+			$spent = $wpdb->get_var( apply_filters( 'woocommerce_customer_get_total_spent_query', $query, $customer ) );
 
 			if ( ! $spent ) {
 				$spent = 0;
diff --git a/includes/data-stores/class-wc-order-data-store-cpt.php b/includes/data-stores/class-wc-order-data-store-cpt.php
index 2cc5b7e1fcd..316aa4b8373 100644
--- a/includes/data-stores/class-wc-order-data-store-cpt.php
+++ b/includes/data-stores/class-wc-order-data-store-cpt.php
@@ -107,10 +107,17 @@ class WC_Order_Data_Store_CPT extends Abstract_WC_Order_Data_Store_CPT implement
 			$date_paid = get_post_meta( $id, '_paid_date', true );
 		}
 
+		// On WC 3.5.0 the ID of the user that placed the order was moved from the post meta _customer_user to the post_author field in the wp_posts table.
+		if ( version_compare( get_option( 'woocommerce_db_version' ), '3.5.0', '>=' ) ) {
+			$customer_id = $post_object->post_author;
+		} else {
+			$customer_id = get_post_meta( $id, '_customer_user', true );
+		}
+
 		$order->set_props(
 			array(
 				'order_key'            => get_post_meta( $id, '_order_key', true ),
-				'customer_id'          => get_post_meta( $id, '_customer_user', true ),
+				'customer_id'          => $customer_id,
 				'billing_first_name'   => get_post_meta( $id, '_billing_first_name', true ),
 				'billing_last_name'    => get_post_meta( $id, '_billing_last_name', true ),
 				'billing_company'      => get_post_meta( $id, '_billing_company', true ),
@@ -258,10 +265,9 @@ class WC_Order_Data_Store_CPT extends Abstract_WC_Order_Data_Store_CPT implement
 			update_post_meta( $id, '_shipping_address_index', implode( ' ', $order->get_address( 'shipping' ) ) );
 		}
 
-		// If customer changed, update any downloadable permissions.
-		if ( in_array( 'customer_id', $updated_props, true ) || in_array( 'billing_email', $updated_props, true ) ) {
-			$data_store = WC_Data_Store::load( 'customer-download' );
-			$data_store->update_user_by_order_id( $id, $order->get_customer_id(), $order->get_billing_email() );
+		// If customer email changed, update any downloadable permissions.
+		if ( in_array( 'billing_email', $updated_props ) ) {
+			$this->update_downloadable_permissions( $order );
 		}
 
 		// Mark user account as active.
@@ -645,6 +651,11 @@ class WC_Order_Data_Store_CPT extends Abstract_WC_Order_Data_Store_CPT implement
 			'page'           => 'paged',
 		);
 
+		// On WC 3.5.0 the ID of the user that placed the order was moved from the post meta _customer_user to the post_author field in the wp_posts table.
+		if ( version_compare( get_option( 'woocommerce_db_version' ), '3.5.0', '>=' ) ) {
+			$key_mapping['customer_id'] = 'author';
+		}
+
 		foreach ( $key_mapping as $query_key => $db_key ) {
 			if ( isset( $query_vars[ $query_key ] ) ) {
 				$query_vars[ $db_key ] = $query_vars[ $query_key ];
diff --git a/includes/emails/class-wc-email.php b/includes/emails/class-wc-email.php
index c7d72fa3bc4..fd36a929e90 100644
--- a/includes/emails/class-wc-email.php
+++ b/includes/emails/class-wc-email.php
@@ -510,28 +510,45 @@ class WC_Email extends WC_Settings_API {
 	/**
 	 * Apply inline styles to dynamic content.
 	 *
+	 * We only inline CSS for html emails, and to do so we use Emogrifier library (if supported).
+	 *
 	 * @param string|null $content Content that will receive inline styles.
 	 * @return string
 	 */
 	public function style_inline( $content ) {
-		// make sure we only inline CSS for html emails.
-		if ( in_array( $this->get_content_type(), array( 'text/html', 'multipart/alternative' ), true ) && class_exists( 'DOMDocument' ) ) {
+		if ( in_array( $this->get_content_type(), array( 'text/html', 'multipart/alternative' ), true ) ) {
 			ob_start();
 			wc_get_template( 'emails/email-styles.php' );
 			$css = apply_filters( 'woocommerce_email_styles', ob_get_clean() );
 
-			// apply CSS styles inline for picky email clients.
-			try {
-				$emogrifier = new Emogrifier( $content, $css );
-				$content    = $emogrifier->emogrify();
-			} catch ( Exception $e ) {
-				$logger = wc_get_logger();
-				$logger->error( $e->getMessage(), array( 'source' => 'emogrifier' ) );
+			if ( $this->supports_emogrifier() ) {
+				if ( ! class_exists( 'Emogrifier' ) ) {
+					include_once dirname( dirname( __FILE__ ) ) . '/libraries/class-emogrifier.php';
+				}
+				try {
+					$emogrifier = new Emogrifier( $content, $css );
+					$content    = $emogrifier->emogrify();
+				} catch ( Exception $e ) {
+					$logger = wc_get_logger();
+					$logger->error( $e->getMessage(), array( 'source' => 'emogrifier' ) );
+				}
+			} else {
+				$content = '<style type="text/css">' . $css . '</style>' . $content;
 			}
 		}
 		return $content;
 	}
 
+	/**
+	 * Return if emogrifier library is supported.
+	 *
+	 * @since 3.5.0
+	 * @return bool
+	 */
+	protected function supports_emogrifier() {
+		return class_exists( 'DOMDocument' ) && version_compare( PHP_VERSION, '5.5', '>=' );
+	}
+
 	/**
 	 * Get the email content in plain text format.
 	 *
diff --git a/includes/libraries/class-emogrifier.php b/includes/libraries/class-emogrifier.php
index 490c2586ce2..12d6c82722a 100644
--- a/includes/libraries/class-emogrifier.php
+++ b/includes/libraries/class-emogrifier.php
@@ -4,1552 +4,1808 @@
  *
  * For more information, please see the README.md file.
  *
- * @version 1.2.0
+ * @version 2.0.0
  *
  * @author Cameron Brooks
  * @author Jaime Prado
- * @author Oliver Klee <typo3-coding@oliverklee.de>
+ * @author Oliver Klee <github@oliverklee.de>
  * @author Roman Ožana <ozana@omdesign.cz>
  * @author Sander Kruger <s.kruger@invessel.com>
+ * @author Zoli Szabó <zoli.szabo+github@gmail.com>
  */
-// @codingStandardsIgnoreFile
 class Emogrifier
 {
-	/**
-	 * @var int
-	 */
-	const CACHE_KEY_CSS = 0;
-
-	/**
-	 * @var int
-	 */
-	const CACHE_KEY_SELECTOR = 1;
-
-	/**
-	 * @var int
-	 */
-	const CACHE_KEY_XPATH = 2;
-
-	/**
-	 * @var int
-	 */
-	const CACHE_KEY_CSS_DECLARATIONS_BLOCK = 3;
-
-	/**
-	 * @var int
-	 */
-	const CACHE_KEY_COMBINED_STYLES = 4;
-
-	/**
-	 * for calculating nth-of-type and nth-child selectors
-	 *
-	 * @var int
-	 */
-	const INDEX = 0;
-
-	/**
-	 * for calculating nth-of-type and nth-child selectors
-	 *
-	 * @var int
-	 */
-	const MULTIPLIER = 1;
-
-	/**
-	 * @var string
-	 */
-	const ID_ATTRIBUTE_MATCHER = '/(\\w+)?\\#([\\w\\-]+)/';
-
-	/**
-	 * @var string
-	 */
-	const CLASS_ATTRIBUTE_MATCHER = '/(\\w+|[\\*\\]])?((\\.[\\w\\-]+)+)/';
-
-	/**
-	 * @var string
-	 */
-	const CONTENT_TYPE_META_TAG = '<meta http-equiv="Content-Type" content="text/html; charset=utf-8">';
-
-	/**
-	 * @var string
-	 */
-	const DEFAULT_DOCUMENT_TYPE = '<!DOCTYPE html>';
-
-	/**
-	 * @var string
-	 */
-	private $html = '';
-
-	/**
-	 * @var string
-	 */
-	private $css = '';
-
-	/**
-	 * @var bool[]
-	 */
-	private $excludedSelectors = array();
-
-	/**
-	 * @var string[]
-	 */
-	private $unprocessableHtmlTags = array( 'wbr' );
-
-	/**
-	 * @var bool[]
-	 */
-	private $allowedMediaTypes = array( 'all' => true, 'screen' => true, 'print' => true );
-
-	/**
-	 * @var mixed[]
-	 */
-	private $caches = array(
-		self::CACHE_KEY_CSS => array(),
-		self::CACHE_KEY_SELECTOR => array(),
-		self::CACHE_KEY_XPATH => array(),
-		self::CACHE_KEY_CSS_DECLARATIONS_BLOCK => array(),
-		self::CACHE_KEY_COMBINED_STYLES => array(),
-	);
-
-	/**
-	 * the visited nodes with the XPath paths as array keys
-	 *
-	 * @var \DOMElement[]
-	 */
-	private $visitedNodes = array();
-
-	/**
-	 * the styles to apply to the nodes with the XPath paths as array keys for the outer array
-	 * and the attribute names/values as key/value pairs for the inner array
-	 *
-	 * @var string[][]
-	 */
-	private $styleAttributesForNodes = array();
-
-	/**
-	 * Determines whether the "style" attributes of tags in the the HTML passed to this class should be preserved.
-	 * If set to false, the value of the style attributes will be discarded.
-	 *
-	 * @var bool
-	 */
-	private $isInlineStyleAttributesParsingEnabled = true;
-
-	/**
-	 * Determines whether the <style> blocks in the HTML passed to this class should be parsed.
-	 *
-	 * If set to true, the <style> blocks will be removed from the HTML and their contents will be applied to the HTML
-	 * via inline styles.
-	 *
-	 * If set to false, the <style> blocks will be left as they are in the HTML.
-	 *
-	 * @var bool
-	 */
-	private $isStyleBlocksParsingEnabled = true;
-
-	/**
-	 * Determines whether elements with the `display: none` property are
-	 * removed from the DOM.
-	 *
-	 * @var bool
-	 */
-	private $shouldKeepInvisibleNodes = true;
-
-	/**
-	 * @var string[]
-	 */
-	private $xPathRules = array(
-		// child
-		'/\\s*>\\s*/'                              => '/',
-		// adjacent sibling
-		'/\\s+\\+\\s+/'                            => '/following-sibling::*[1]/self::',
-		// descendant
-		'/\\s+(?=.*[^\\]]{1}$)/'                   => '//',
-		// :first-child
-		'/([^\\/]+):first-child/i'                 => '*[1]/self::\\1',
-		// :last-child
-		'/([^\\/]+):last-child/i'                  => '*[last()]/self::\\1',
-		// attribute only
-		'/^\\[(\\w+|\\w+\\=[\'"]?\\w+[\'"]?)\\]/'  => '*[@\\1]',
-		// attribute
-		'/(\\w)\\[(\\w+)\\]/'                      => '\\1[@\\2]',
-		// exact attribute
-		'/(\\w)\\[(\\w+)\\=[\'"]?([\\w\\s]+)[\'"]?\\]/' => '\\1[@\\2="\\3"]',
-		// element attribute~=
-		'/([\\w\\*]+)\\[(\\w+)[\\s]*\\~\\=[\\s]*[\'"]?([\\w-_\\/]+)[\'"]?\\]/'
-			=> '\\1[contains(concat(" ", @\\2, " "), concat(" ", "\\3", " "))]',
-		// element attribute^=
-		'/([\\w\\*]+)\\[(\\w+)[\\s]*\\^\\=[\\s]*[\'"]?([\\w-_\\/]+)[\'"]?\\]/' => '\\1[starts-with(@\\2, "\\3")]',
-		// element attribute*=
-		'/([\\w\\*]+)\\[(\\w+)[\\s]*\\*\\=[\\s]*[\'"]?([\\w-_\\s\\/:;]+)[\'"]?\\]/' => '\\1[contains(@\\2, "\\3")]',
-		// element attribute$=
-		'/([\\w\\*]+)\\[(\\w+)[\\s]*\\$\\=[\\s]*[\'"]?([\\w-_\\s\\/]+)[\'"]?\\]/'
-			=> '\\1[substring(@\\2, string-length(@\\2) - string-length("\\3") + 1) = "\\3"]',
-		// element attribute|=
-		'/([\\w\\*]+)\\[(\\w+)[\\s]*\\|\\=[\\s]*[\'"]?([\\w-_\\s\\/]+)[\'"]?\\]/'
-			=> '\\1[@\\2="\\3" or starts-with(@\\2, concat("\\3", "-"))]',
-	);
-
-	/**
-	 * Determines whether CSS styles that have an equivalent HTML attribute
-	 * should be mapped and attached to those elements.
-	 *
-	 * @var bool
-	 */
-	private $shouldMapCssToHtml = false;
-
-	/**
-	 * This multi-level array contains simple mappings of CSS properties to
-	 * HTML attributes. If a mapping only applies to certain HTML nodes or
-	 * only for certain values, the mapping is an object with a whitelist
-	 * of nodes and values.
-	 *
-	 * @var mixed[][]
-	 */
-	private $cssToHtmlMap = array(
-		'background-color' => array(
-			'attribute' => 'bgcolor',
-		),
-		'text-align' => array(
-			'attribute' => 'align',
-			'nodes' => array('p', 'div', 'td'),
-			'values' => array('left', 'right', 'center', 'justify'),
-		),
-		'float' => array(
-			'attribute' => 'align',
-			'nodes' => array('table', 'img'),
-			'values' => array('left', 'right'),
-		),
-		'border-spacing' => array(
-			'attribute' => 'cellspacing',
-			'nodes' => array('table'),
-		),
-	);
-
-	public static $_media = '';
-
-	/**
-	 * The constructor.
-	 *
-	 * @param string $html the HTML to emogrify, must be UTF-8-encoded
-	 * @param string $css the CSS to merge, must be UTF-8-encoded
-	 */
-	public function __construct($html = '', $css = '')
-	{
-		$this->setHtml($html);
-		$this->setCss($css);
-	}
-
-	/**
-	 * The destructor.
-	 */
-	public function __destruct()
-	{
-		$this->purgeVisitedNodes();
-	}
-
-	/**
-	 * Sets the HTML to emogrify.
-	 *
-	 * @param string $html the HTML to emogrify, must be UTF-8-encoded
-	 *
-	 * @return void
-	 */
-	public function setHtml($html)
-	{
-		$this->html = $html;
-	}
-
-	/**
-	 * Sets the CSS to merge with the HTML.
-	 *
-	 * @param string $css the CSS to merge, must be UTF-8-encoded
-	 *
-	 * @return void
-	 */
-	public function setCss($css)
-	{
-		$this->css = $css;
-	}
-
-	/**
-	 * Applies $this->css to $this->html and returns the HTML with the CSS
-	 * applied.
-	 *
-	 * This method places the CSS inline.
-	 *
-	 * @return string
-	 *
-	 * @throws \BadMethodCallException
-	 */
-	public function emogrify()
-	{
-		if ($this->html === '') {
-			throw new BadMethodCallException('Please set some HTML first before calling emogrify.', 1390393096);
-		}
-
-		self::$_media = ''; // reset.
-
-		$xmlDocument = $this->createXmlDocument();
-		$this->process($xmlDocument);
-
-		return $xmlDocument->saveHTML();
-	}
-
-	/**
-	 * Applies $this->css to $this->html and returns only the HTML content
-	 * within the <body> tag.
-	 *
-	 * This method places the CSS inline.
-	 *
-	 * @return string
-	 *
-	 * @throws \BadMethodCallException
-	 */
-	public function emogrifyBodyContent()
-	{
-		if ($this->html === '') {
-			throw new BadMethodCallException('Please set some HTML first before calling emogrify.', 1390393096);
-		}
-
-		$xmlDocument = $this->createXmlDocument();
-		$this->process($xmlDocument);
-
-		$innerDocument = new DOMDocument();
-		foreach ($xmlDocument->documentElement->getElementsByTagName('body')->item(0)->childNodes as $childNode) {
-			$innerDocument->appendChild($innerDocument->importNode($childNode, true));
-		}
-
-		return html_entity_decode($innerDocument->saveHTML());
-	}
-
-	/**
-	 * Applies $this->css to $xmlDocument.
-	 *
-	 * This method places the CSS inline.
-	 *
-	 * @param \DOMDocument $xmlDocument
-	 *
-	 * @return void
-	 *
-	 * @throws \InvalidArgumentException
-	 */
-	protected function process(DOMDocument $xmlDocument)
-	{
-		$xPath = new DOMXPath($xmlDocument);
-		$this->clearAllCaches();
-
-		// Before be begin processing the CSS file, parse the document and normalize all existing CSS attributes.
-		// This changes 'DISPLAY: none' to 'display: none'.
-		// We wouldn't have to do this if DOMXPath supported XPath 2.0.
-		// Also store a reference of nodes with existing inline styles so we don't overwrite them.
-		$this->purgeVisitedNodes();
-
-		set_error_handler(array($this, 'handleXpathError'), E_WARNING);
-
-		$nodesWithStyleAttributes = $xPath->query('//*[@style]');
-		if ($nodesWithStyleAttributes !== false) {
-			/** @var \DOMElement $node */
-			foreach ($nodesWithStyleAttributes as $node) {
-				if ($this->isInlineStyleAttributesParsingEnabled) {
-					$this->normalizeStyleAttributes($node);
-				} else {
-					$node->removeAttribute('style');
-				}
-			}
-		}
-
-		// grab any existing style blocks from the html and append them to the existing CSS
-		// (these blocks should be appended so as to have precedence over conflicting styles in the existing CSS)
-		$allCss = $this->css;
-
-		if ($this->isStyleBlocksParsingEnabled) {
-			$allCss .= $this->getCssFromAllStyleNodes($xPath);
-		}
-
-		$cssParts = $this->splitCssAndMediaQuery($allCss);
-		$excludedNodes = $this->getNodesToExclude($xPath);
-		$cssRules = $this->parseCssRules($cssParts['css']);
-		foreach ($cssRules as $cssRule) {
-			// query the body for the xpath selector
-			$nodesMatchingCssSelectors = $xPath->query($this->translateCssToXpath($cssRule['selector']));
-			// ignore invalid selectors
-			if ($nodesMatchingCssSelectors === false) {
-				continue;
-			}
-
-			/** @var \DOMElement $node */
-			foreach ($nodesMatchingCssSelectors as $node) {
-				if (in_array($node, $excludedNodes, true)) {
-					continue;
-				}
-
-				// if it has a style attribute, get it, process it, and append (overwrite) new stuff
-				if ($node->hasAttribute('style')) {
-					// break it up into an associative array
-					$oldStyleDeclarations = $this->parseCssDeclarationsBlock($node->getAttribute('style'));
-				} else {
-					$oldStyleDeclarations = array();
-				}
-				$newStyleDeclarations = $this->parseCssDeclarationsBlock($cssRule['declarationsBlock']);
-				if ($this->shouldMapCssToHtml) {
-					$this->mapCssToHtmlAttributes($newStyleDeclarations, $node);
-				}
-				$node->setAttribute(
-					'style',
-					$this->generateStyleStringFromDeclarationsArrays($oldStyleDeclarations, $newStyleDeclarations)
-				);
-			}
-		}
-
-		restore_error_handler();
-
-		if ($this->isInlineStyleAttributesParsingEnabled) {
-			$this->fillStyleAttributesWithMergedStyles();
-		}
-
-		if ($this->shouldKeepInvisibleNodes) {
-			$this->removeInvisibleNodes($xPath);
-		}
-
-		$this->copyCssWithMediaToStyleNode($xmlDocument, $xPath, $cssParts['media']);
-	}
-
-	/**
-	 * Applies $styles to $node.
-	 *
-	 * This method maps CSS styles to HTML attributes and adds those to the
-	 * node.
-	 *
-	 * @param string[] $styles the new CSS styles taken from the global styles to be applied to this node
-	 * @param \DOMNode $node   node to apply styles to
-	 *
-	 * @return void
-	 */
-	private function mapCssToHtmlAttributes(array $styles, DOMNode $node)
-	{
-		foreach ($styles as $property => $value) {
-			// Strip !important indicator
-			$value = trim(str_replace('!important', '', $value));
-			$this->mapCssToHtmlAttribute($property, $value, $node);
-		}
-	}
-
-	/**
-	 * Tries to apply the CSS style to $node as an attribute.
-	 *
-	 * This method maps a CSS rule to HTML attributes and adds those to the node.
-	 *
-	 * @param string $property the name of the CSS property to map
-	 * @param string $value    the value of the style rule to map
-	 * @param \DOMNode $node   node to apply styles to
-	 *
-	 * @return void
-	 */
-	private function mapCssToHtmlAttribute($property, $value, DOMNode $node)
-	{
-		if (!$this->mapSimpleCssProperty($property, $value, $node)) {
-			$this->mapComplexCssProperty($property, $value, $node);
-		}
-	}
-
-	/**
-	 * Looks up the CSS property in the mapping table and maps it if it matches the conditions.
-	 *
-	 * @param string $property the name of the CSS property to map
-	 * @param string $value    the value of the style rule to map
-	 * @param \DOMNode $node   node to apply styles to
-	 *
-	 * @return bool true if the property cab be mapped using the simple mapping table
-	 */
-	private function mapSimpleCssProperty($property, $value, DOMNode $node)
-	{
-		if (!isset($this->cssToHtmlMap[$property])) {
-			return false;
-		}
-
-		$mapping = $this->cssToHtmlMap[$property];
-		$nodesMatch = !isset($mapping['nodes']) || in_array($node->nodeName, $mapping['nodes'], true);
-		$valuesMatch = !isset($mapping['values']) || in_array($value, $mapping['values'], true);
-		if (!$nodesMatch || !$valuesMatch) {
-			return false;
-		}
-
-		$node->setAttribute($mapping['attribute'], $value);
-
-		return true;
-	}
-
-	/**
-	 * Maps CSS properties that need special transformation to an HTML attribute.
-	 *
-	 * @param string $property the name of the CSS property to map
-	 * @param string $value    the value of the style rule to map
-	 * @param \DOMNode $node   node to apply styles to
-	 *
-	 * @return void
-	 */
-	private function mapComplexCssProperty($property, $value, DOMNode $node)
-	{
-		$nodeName = $node->nodeName;
-		$isTable = $nodeName === 'table';
-		$isImage = $nodeName === 'img';
-		$isTableOrImage = $isTable || $isImage;
-
-		switch ($property) {
-			case 'background':
-				// Parse out the color, if any
-				$styles = explode(' ', $value);
-				$first = $styles[0];
-				if (!is_numeric(substr($first, 0, 1)) && substr($first, 0, 3) !== 'url') {
-					// This is not a position or image, assume it's a color
-					$node->setAttribute('bgcolor', $first);
-				}
-				break;
-			case 'width':
-				// intentional fall-through
-			case 'height':
-				// Only parse values in px and %, but not values like "auto".
-				if (preg_match('/^\d+(px|%)$/', $value)) {
-					// Remove 'px'. This regex only conserves numbers and %
-					$number = preg_replace('/[^0-9.%]/', '', $value);
-					$node->setAttribute($property, $number);
-				}
-				break;
-			case 'margin':
-				if ($isTableOrImage) {
-					$margins = $this->parseCssShorthandValue($value);
-					if ($margins['left'] === 'auto' && $margins['right'] === 'auto') {
-						$node->setAttribute('align', 'center');
-					}
-				}
-				break;
-			case 'border':
-				if ($isTableOrImage) {
-					if ($value === 'none' || $value === '0') {
-						$node->setAttribute('border', '0');
-					}
-				}
-				break;
-			default:
-		}
-	}
-
-	/**
-	 * Parses a shorthand CSS value and splits it into individual values
-	 *
-	 * @param string $value a string of CSS value with 1, 2, 3 or 4 sizes
-	 *                      For example: padding: 0 auto;
-	 *                      '0 auto' is split into top: 0, left: auto, bottom: 0,
-	 *                      right: auto.
-	 *
-	 * @return string[] an array of values for top, right, bottom and left (using these as associative array keys)
-	 */
-	private function parseCssShorthandValue($value)
-	{
-		$values = preg_split('/\\s+/', $value);
-
-		$css = array();
-		$css['top'] = $values[0];
-		$css['right'] = (count($values) > 1) ? $values[1] : $css['top'];
-		$css['bottom'] = (count($values) > 2) ? $values[2] : $css['top'];
-		$css['left'] = (count($values) > 3) ? $values[3] : $css['right'];
-
-		return $css;
-	}
-
-	/**
-	 * Extracts and parses the individual rules from a CSS string.
-	 *
-	 * @param string $css a string of raw CSS code
-	 *
-	 * @return string[][] an array of string sub-arrays with the keys
-	 *         "selector" (the CSS selector(s), e.g., "*" or "h1"),
-	 *         "declarationsBLock" (the semicolon-separated CSS declarations for that selector(s),
-	 *         e.g., "color: red; height: 4px;"),
-	 *         and "line" (the line number e.g. 42)
-	 */
-	private function parseCssRules($css)
-	{
-		$cssKey = md5($css);
-		if (!isset($this->caches[self::CACHE_KEY_CSS][$cssKey])) {
-			// process the CSS file for selectors and definitions
-			preg_match_all('/(?:^|[\\s^{}]*)([^{]+){([^}]*)}/mis', $css, $matches, PREG_SET_ORDER);
-
-			$cssRules = array();
-			/** @var string[] $cssRule */
-			foreach ($matches as $key => $cssRule) {
-				$cssDeclaration = trim($cssRule[2]);
-				if ($cssDeclaration === '') {
-					continue;
-				}
-
-				$selectors = explode(',', $cssRule[1]);
-				foreach ($selectors as $selector) {
-					// don't process pseudo-elements and behavioral (dynamic) pseudo-classes;
-					// only allow structural pseudo-classes
-					$hasPseudoElement = strpos($selector, '::') !== false;
-					$hasAnyPseudoClass = (bool) preg_match('/:[a-zA-Z]/', $selector);
-					$hasSupportedPseudoClass = (bool) preg_match('/:\\S+\\-(child|type\\()/i', $selector);
-					if ($hasPseudoElement || ($hasAnyPseudoClass && !$hasSupportedPseudoClass)) {
-						continue;
-					}
-
-					$cssRules[] = array(
-						'selector' => trim($selector),
-						'declarationsBlock' => $cssDeclaration,
-						// keep track of where it appears in the file, since order is important
-						'line' => $key,
-					);
-				}
-			}
-
-			usort($cssRules, array($this, 'sortBySelectorPrecedence'));
-
-			$this->caches[self::CACHE_KEY_CSS][$cssKey] = $cssRules;
-		}
-
-		return $this->caches[self::CACHE_KEY_CSS][$cssKey];
-	}
-
-	/**
-	 * Disables the parsing of inline styles.
-	 *
-	 * @return void
-	 */
-	public function disableInlineStyleAttributesParsing()
-	{
-		$this->isInlineStyleAttributesParsingEnabled = false;
-	}
-
-	/**
-	 * Disables the parsing of <style> blocks.
-	 *
-	 * @return void
-	 */
-	public function disableStyleBlocksParsing()
-	{
-		$this->isStyleBlocksParsingEnabled = false;
-	}
-
-	/**
-	 * Disables the removal of elements with `display: none` properties.
-	 *
-	 * @return void
-	 */
-	public function disableInvisibleNodeRemoval()
-	{
-		$this->shouldKeepInvisibleNodes = false;
-	}
-
-	/**
-	 * Enables the attachment/override of HTML attributes for which a
-	 * corresponding CSS property has been set.
-	 *
-	 * @return void
-	 */
-	public function enableCssToHtmlMapping()
-	{
-		$this->shouldMapCssToHtml = true;
-	}
-
-	/**
-	 * Clears all caches.
-	 *
-	 * @return void
-	 */
-	private function clearAllCaches()
-	{
-		$this->clearCache(self::CACHE_KEY_CSS);
-		$this->clearCache(self::CACHE_KEY_SELECTOR);
-		$this->clearCache(self::CACHE_KEY_XPATH);
-		$this->clearCache(self::CACHE_KEY_CSS_DECLARATIONS_BLOCK);
-		$this->clearCache(self::CACHE_KEY_COMBINED_STYLES);
-	}
-
-	/**
-	 * Clears a single cache by key.
-	 *
-	 * @param int $key the cache key, must be CACHE_KEY_CSS, CACHE_KEY_SELECTOR, CACHE_KEY_XPATH
-	 *                 or CACHE_KEY_CSS_DECLARATION_BLOCK
-	 *
-	 * @return void
-	 *
-	 * @throws \InvalidArgumentException
-	 */
-	private function clearCache($key)
-	{
-		$allowedCacheKeys = array(
-			self::CACHE_KEY_CSS,
-			self::CACHE_KEY_SELECTOR,
-			self::CACHE_KEY_XPATH,
-			self::CACHE_KEY_CSS_DECLARATIONS_BLOCK,
-			self::CACHE_KEY_COMBINED_STYLES,
-		);
-		if (!in_array($key, $allowedCacheKeys, true)) {
-			throw new InvalidArgumentException('Invalid cache key: ' . $key, 1391822035);
-		}
-
-		$this->caches[$key] = array();
-	}
-
-	/**
-	 * Purges the visited nodes.
-	 *
-	 * @return void
-	 */
-	private function purgeVisitedNodes()
-	{
-		$this->visitedNodes = array();
-		$this->styleAttributesForNodes = array();
-	}
-
-	/**
-	 * Marks a tag for removal.
-	 *
-	 * There are some HTML tags that DOMDocument cannot process, and it will throw an error if it encounters them.
-	 * In particular, DOMDocument will complain if you try to use HTML5 tags in an XHTML document.
-	 *
-	 * Note: The tags will not be removed if they have any content.
-	 *
-	 * @param string $tagName the tag name, e.g., "p"
-	 *
-	 * @return void
-	 */
-	public function addUnprocessableHtmlTag($tagName)
-	{
-		$this->unprocessableHtmlTags[] = $tagName;
-	}
-
-	/**
-	 * Drops a tag from the removal list.
-	 *
-	 * @param string $tagName the tag name, e.g., "p"
-	 *
-	 * @return void
-	 */
-	public function removeUnprocessableHtmlTag($tagName)
-	{
-		$key = array_search($tagName, $this->unprocessableHtmlTags, true);
-		if ($key !== false) {
-			unset($this->unprocessableHtmlTags[$key]);
-		}
-	}
-
-	/**
-	 * Marks a media query type to keep.
-	 *
-	 * @param string $mediaName the media type name, e.g., "braille"
-	 *
-	 * @return void
-	 */
-	public function addAllowedMediaType($mediaName)
-	{
-		$this->allowedMediaTypes[$mediaName] = true;
-	}
-
-	/**
-	 * Drops a media query type from the allowed list.
-	 *
-	 * @param string $mediaName the tag name, e.g., "braille"
-	 *
-	 * @return void
-	 */
-	public function removeAllowedMediaType($mediaName)
-	{
-		if (isset($this->allowedMediaTypes[$mediaName])) {
-			unset($this->allowedMediaTypes[$mediaName]);
-		}
-	}
-
-	/**
-	 * Adds a selector to exclude nodes from emogrification.
-	 *
-	 * Any nodes that match the selector will not have their style altered.
-	 *
-	 * @param string $selector the selector to exclude, e.g., ".editor"
-	 *
-	 * @return void
-	 */
-	public function addExcludedSelector($selector)
-	{
-		$this->excludedSelectors[$selector] = true;
-	}
-
-	/**
-	 * No longer excludes the nodes matching this selector from emogrification.
-	 *
-	 * @param string $selector the selector to no longer exclude, e.g., ".editor"
-	 *
-	 * @return void
-	 */
-	public function removeExcludedSelector($selector)
-	{
-		if (isset($this->excludedSelectors[$selector])) {
-			unset($this->excludedSelectors[$selector]);
-		}
-	}
-
-	/**
-	 * This removes styles from your email that contain display:none.
-	 * We need to look for display:none, but we need to do a case-insensitive search. Since DOMDocument only
-	 * supports XPath 1.0, lower-case() isn't available to us. We've thus far only set attributes to lowercase,
-	 * not attribute values. Consequently, we need to translate() the letters that would be in 'NONE' ("NOE")
-	 * to lowercase.
-	 *
-	 * @param \DOMXPath $xPath
-	 *
-	 * @return void
-	 */
-	private function removeInvisibleNodes(DOMXPath $xPath)
-	{
-		$nodesWithStyleDisplayNone = $xPath->query(
-			'//*[contains(translate(translate(@style," ",""),"NOE","noe"),"display:none")]'
-		);
-		if ($nodesWithStyleDisplayNone->length === 0) {
-			return;
-		}
-
-		// The checks on parentNode and is_callable below ensure that if we've deleted the parent node,
-		// we don't try to call removeChild on a nonexistent child node
-		/** @var \DOMNode $node */
-		foreach ($nodesWithStyleDisplayNone as $node) {
-			if ($node->parentNode && is_callable(array($node->parentNode, 'removeChild'))) {
-				$node->parentNode->removeChild($node);
-			}
-		}
-	}
-
-	private function normalizeStyleAttributes_callback( $m ) {
-		return strtolower( $m[0] );
-	}
-
-	/**
-	 * Normalizes the value of the "style" attribute and saves it.
-	 *
-	 * @param \DOMElement $node
-	 *
-	 * @return void
-	 */
-	private function normalizeStyleAttributes(DOMElement $node)
-	{
-		$normalizedOriginalStyle = preg_replace_callback(
-			'/[A-z\\-]+(?=\\:)/S',
-			array( $this, 'normalizeStyleAttributes_callback' ),
-			$node->getAttribute('style')
-		);
-
-		// in order to not overwrite existing style attributes in the HTML, we
-		// have to save the original HTML styles
-		$nodePath = $node->getNodePath();
-		if (!isset($this->styleAttributesForNodes[$nodePath])) {
-			$this->styleAttributesForNodes[$nodePath] = $this->parseCssDeclarationsBlock($normalizedOriginalStyle);
-			$this->visitedNodes[$nodePath] = $node;
-		}
-
-		$node->setAttribute('style', $normalizedOriginalStyle);
-	}
-
-	/**
-	 * Merges styles from styles attributes and style nodes and applies them to the attribute nodes
-	 *
-	 * @return void
-	 */
-	private function fillStyleAttributesWithMergedStyles()
-	{
-		foreach ($this->styleAttributesForNodes as $nodePath => $styleAttributesForNode) {
-			$node = $this->visitedNodes[$nodePath];
-			$currentStyleAttributes = $this->parseCssDeclarationsBlock($node->getAttribute('style'));
-			$node->setAttribute(
-				'style',
-				$this->generateStyleStringFromDeclarationsArrays(
-					$currentStyleAttributes,
-					$styleAttributesForNode
-				)
-			);
-		}
-	}
-
-	/**
-	 * This method merges old or existing name/value array with new name/value array
-	 * and then generates a string of the combined style suitable for placing inline.
-	 * This becomes the single point for CSS string generation allowing for consistent
-	 * CSS output no matter where the CSS originally came from.
-	 *
-	 * @param string[] $oldStyles
-	 * @param string[] $newStyles
-	 *
-	 * @return string
-	 */
-	private function generateStyleStringFromDeclarationsArrays(array $oldStyles, array $newStyles)
-	{
-		$combinedStyles = array_merge($oldStyles, $newStyles);
-		$cacheKey = serialize($combinedStyles);
-		if (isset($this->caches[self::CACHE_KEY_COMBINED_STYLES][$cacheKey])) {
-			return $this->caches[self::CACHE_KEY_COMBINED_STYLES][$cacheKey];
-		}
-
-		foreach ($oldStyles as $attributeName => $attributeValue) {
-			if (!isset($newStyles[$attributeName])) {
-				continue;
-			}
-
-			$newAttributeValue = $newStyles[$attributeName];
-			if ($this->attributeValueIsImportant($attributeValue)
-				&& !$this->attributeValueIsImportant($newAttributeValue)
-			) {
-				$combinedStyles[$attributeName] = $attributeValue;
-			}
-		}
-
-		$style = '';
-		foreach ($combinedStyles as $attributeName => $attributeValue) {
-			$style .= strtolower(trim($attributeName)) . ': ' . trim($attributeValue) . '; ';
-		}
-		$trimmedStyle = rtrim($style);
-
-		$this->caches[self::CACHE_KEY_COMBINED_STYLES][$cacheKey] = $trimmedStyle;
-
-		return $trimmedStyle;
-	}
-
-	/**
-	 * Checks whether $attributeValue is marked as !important.
-	 *
-	 * @param string $attributeValue
-	 *
-	 * @return bool
-	 */
-	private function attributeValueIsImportant($attributeValue)
-	{
-		return strtolower(substr(trim($attributeValue), -10)) === '!important';
-	}
-
-	/**
-	 * Applies $css to $xmlDocument, limited to the media queries that actually apply to the document.
-	 *
-	 * @param \DOMDocument $xmlDocument the document to match against
-	 * @param \DOMXPath $xPath
-	 * @param string $css a string of CSS
-	 *
-	 * @return void
-	 */
-	private function copyCssWithMediaToStyleNode(DOMDocument $xmlDocument, DOMXPath $xPath, $css)
-	{
-		if ($css === '') {
-			return;
-		}
-
-		$mediaQueriesRelevantForDocument = array();
-
-		foreach ($this->extractMediaQueriesFromCss($css) as $mediaQuery) {
-			foreach ($this->parseCssRules($mediaQuery['css']) as $selector) {
-				if ($this->existsMatchForCssSelector($xPath, $selector['selector'])) {
-					$mediaQueriesRelevantForDocument[] = $mediaQuery['query'];
-					break;
-				}
-			}
-		}
-
-		$this->addStyleElementToDocument($xmlDocument, implode($mediaQueriesRelevantForDocument));
-	}
-
-	/**
-	 * Extracts the media queries from $css while skipping empty media queries.
-	 *
-	 * @param string $css
-	 *
-	 * @return string[][] numeric array with string sub-arrays with the keys "css" and "query"
-	 */
-	private function extractMediaQueriesFromCss($css)
-	{
-		preg_match_all('/@media\\b[^{]*({((?:[^{}]+|(?1))*)})/', $css, $rawMediaQueries, PREG_SET_ORDER);
-		$parsedQueries = array();
-
-		foreach ($rawMediaQueries as $mediaQuery) {
-			if ($mediaQuery[2] !== '') {
-				$parsedQueries[] = array(
-					'css'   => $mediaQuery[2],
-					'query' => $mediaQuery[0],
-				);
-			}
-		}
-
-		return $parsedQueries;
-	}
-
-	/**
-	 * Checks whether there is at least one matching element for $cssSelector.
-	 *
-	 * @param \DOMXPath $xPath
-	 * @param string $cssSelector
-	 *
-	 * @return bool
-	 */
-	private function existsMatchForCssSelector(DOMXPath $xPath, $cssSelector)
-	{
-		$nodesMatchingSelector = $xPath->query($this->translateCssToXpath($cssSelector));
-
-		return $nodesMatchingSelector !== false && $nodesMatchingSelector->length !== 0;
-	}
-
-	/**
-	 * Returns CSS content.
-	 *
-	 * @param \DOMXPath $xPath
-	 *
-	 * @return string
-	 */
-	private function getCssFromAllStyleNodes(DOMXPath $xPath)
-	{
-		$styleNodes = $xPath->query('//style');
-
-		if ($styleNodes === false) {
-			return '';
-		}
-
-		$css = '';
-		/** @var \DOMNode $styleNode */
-		foreach ($styleNodes as $styleNode) {
-			$css .= "\n\n" . $styleNode->nodeValue;
-			$styleNode->parentNode->removeChild($styleNode);
-		}
-
-		return $css;
-	}
-
-	/**
-	 * Adds a style element with $css to $document.
-	 *
-	 * This method is protected to allow overriding.
-	 *
-	 * @see https://github.com/jjriv/emogrifier/issues/103
-	 *
-	 * @param \DOMDocument $document
-	 * @param string $css
-	 *
-	 * @return void
-	 */
-	protected function addStyleElementToDocument(DOMDocument $document, $css)
-	{
-		$styleElement = $document->createElement('style', $css);
-		$styleAttribute = $document->createAttribute('type');
-		$styleAttribute->value = 'text/css';
-		$styleElement->appendChild($styleAttribute);
-
-		$head = $this->getOrCreateHeadElement($document);
-		$head->appendChild($styleElement);
-	}
-
-	/**
-	 * Returns the existing or creates a new head element in $document.
-	 *
-	 * @param \DOMDocument $document
-	 *
-	 * @return \DOMNode the head element
-	 */
-	private function getOrCreateHeadElement(DOMDocument $document)
-	{
-		$head = $document->getElementsByTagName('head')->item(0);
-
-		if ($head === null) {
-			$head = $document->createElement('head');
-			$html = $document->getElementsByTagName('html')->item(0);
-			$html->insertBefore($head, $document->getElementsByTagName('body')->item(0));
-		}
-
-		return $head;
-	}
-
-	/**
-	 * Splits input CSS code to an array where:
-	 *
-	 * - key "css" will be contains clean CSS code
-	 * - key "media" will be contains all valuable media queries
-	 *
-	 * Example:
-	 *
-	 * The CSS code
-	 *
-	 *   "@import "file.css"; h1 { color:red; } @media { h1 {}} @media tv { h1 {}}"
-	 *
-	 * will be parsed into the following array:
-	 *
-	 *   "css" => "h1 { color:red; }"
-	 *   "media" => "@media { h1 {}}"
-	 *
-	 * @param string $css
-	 *
-	 * @return string[]
-	 */
-	private function splitCssAndMediaQuery($css)
-	{
-		$cssWithoutComments = preg_replace('/\\/\\*.*\\*\\//sU', '', $css);
-
-		$mediaTypesExpression = '';
-		if (!empty($this->allowedMediaTypes)) {
-			$mediaTypesExpression = '|' . implode('|', array_keys($this->allowedMediaTypes));
-		}
-
-		$cssForAllowedMediaTypes = preg_replace_callback(
-			'#@media\\s+(?:only\\s)?(?:[\\s{\\(]' . $mediaTypesExpression . ')\\s?[^{]+{.*}\\s*}\\s*#misU',
-			array( $this, '_media_concat' ),
-			$cssWithoutComments
-		);
-
-		// filter the CSS
-		$search = array(
-			'import directives' => '/^\\s*@import\\s[^;]+;/misU',
-			'remaining media enclosures' => '/^\\s*@media\\s[^{]+{(.*)}\\s*}\\s/misU',
-		);
-
-		$cleanedCss = preg_replace($search, '', $cssForAllowedMediaTypes);
-
-		return array('css' => $cleanedCss, 'media' => self::$_media);
-	}
-
-	private function _media_concat( $matches ) {
-		self::$_media .= $matches[0];
-	}
-
-	/**
-	 * Creates a DOMDocument instance with the current HTML.
-	 *
-	 * @return \DOMDocument
-	 */
-	private function createXmlDocument()
-	{
-		$xmlDocument = new DOMDocument;
-		$xmlDocument->encoding = 'UTF-8';
-		$xmlDocument->strictErrorChecking = false;
-		$xmlDocument->formatOutput = true;
-		$libXmlState = libxml_use_internal_errors(true);
-		$xmlDocument->loadHTML($this->getUnifiedHtml());
-		libxml_clear_errors();
-		libxml_use_internal_errors($libXmlState);
-		$xmlDocument->normalizeDocument();
-
-		return $xmlDocument;
-	}
-
-	/**
-	 * Returns the HTML with the unprocessable HTML tags removed and
-	 * with added document type and Content-Type meta tag if needed.
-	 *
-	 * @return string the unified HTML
-	 *
-	 * @throws \BadMethodCallException
-	 */
-	private function getUnifiedHtml()
-	{
-		$htmlWithoutUnprocessableTags = $this->removeUnprocessableTags($this->html);
-		$htmlWithDocumentType = $this->ensureDocumentType($htmlWithoutUnprocessableTags);
-
-		return $this->addContentTypeMetaTag($htmlWithDocumentType);
-	}
-
-	/**
-	 * Removes the unprocessable tags from $html (if this feature is enabled).
-	 *
-	 * @param string $html
-	 *
-	 * @return string the reworked HTML with the unprocessable tags removed
-	 */
-	private function removeUnprocessableTags($html)
-	{
-		if (empty($this->unprocessableHtmlTags)) {
-			return $html;
-		}
-
-		$unprocessableHtmlTags = implode('|', $this->unprocessableHtmlTags);
-
-		return preg_replace(
-			'/<\\/?(' . $unprocessableHtmlTags . ')[^>]*>/i',
-			'',
-			$html
-		);
-	}
-
-	/**
-	 * Makes sure that the passed HTML has a document type.
-	 *
-	 * @param string $html
-	 *
-	 * @return string HTML with document type
-	 */
-	private function ensureDocumentType($html)
-	{
-		$hasDocumentType = stripos($html, '<!DOCTYPE') !== false;
-		if ($hasDocumentType) {
-			return $html;
-		}
-
-		return self::DEFAULT_DOCUMENT_TYPE . $html;
-	}
-
-	/**
-	 * Adds a Content-Type meta tag for the charset.
-	 *
-	 * @param string $html
-	 *
-	 * @return string the HTML with the meta tag added
-	 */
-	private function addContentTypeMetaTag($html)
-	{
-		$hasContentTypeMetaTag = stristr($html, 'Content-Type') !== false;
-		if ($hasContentTypeMetaTag) {
-			return $html;
-		}
-
-		// We are trying to insert the meta tag to the right spot in the DOM.
-		// If we just prepended it to the HTML, we would lose attributes set to the HTML tag.
-		$hasHeadTag = stripos($html, '<head') !== false;
-		$hasHtmlTag = stripos($html, '<html') !== false;
-
-		if ($hasHeadTag) {
-			$reworkedHtml = preg_replace('/<head(.*?)>/i', '<head$1>' . self::CONTENT_TYPE_META_TAG, $html);
-		} elseif ($hasHtmlTag) {
-			$reworkedHtml = preg_replace(
-				'/<html(.*?)>/i',
-				'<html$1><head>' . self::CONTENT_TYPE_META_TAG . '</head>',
-				$html
-			);
-		} else {
-			$reworkedHtml = self::CONTENT_TYPE_META_TAG . $html;
-		}
-
-		return $reworkedHtml;
-	}
-
-	/**
-	 * @param string[] $a
-	 * @param string[] $b
-	 *
-	 * @return int
-	 */
-	private function sortBySelectorPrecedence(array $a, array $b)
-	{
-		$precedenceA = $this->getCssSelectorPrecedence($a['selector']);
-		$precedenceB = $this->getCssSelectorPrecedence($b['selector']);
-
-		// We want these sorted in ascending order so selectors with lesser precedence get processed first and
-		// selectors with greater precedence get sorted last.
-		$precedenceForEquals = ($a['line'] < $b['line'] ? -1 : 1);
-		$precedenceForNotEquals = ($precedenceA < $precedenceB ? -1 : 1);
-		return ($precedenceA === $precedenceB) ? $precedenceForEquals : $precedenceForNotEquals;
-	}
-
-	/**
-	 * @param string $selector
-	 *
-	 * @return int
-	 */
-	private function getCssSelectorPrecedence($selector)
-	{
-		$selectorKey = md5($selector);
-		if (!isset($this->caches[self::CACHE_KEY_SELECTOR][$selectorKey])) {
-			$precedence = 0;
-			$value = 100;
-			// ids: worth 100, classes: worth 10, elements: worth 1
-			$search = array('\\#','\\.','');
-
-			foreach ($search as $s) {
-				if (trim($selector) === '') {
-					break;
-				}
-				$number = 0;
-				$selector = preg_replace('/' . $s . '\\w+/', '', $selector, -1, $number);
-				$precedence += ($value * $number);
-				$value /= 10;
-			}
-			$this->caches[self::CACHE_KEY_SELECTOR][$selectorKey] = $precedence;
-		}
-
-		return $this->caches[self::CACHE_KEY_SELECTOR][$selectorKey];
-	}
-
-	private function translateCssToXpath_callback( $matches ) {
-		return strtolower($matches[0]);
-	}
-
-	/**
-	 * Maps a CSS selector to an XPath query string.
-	 *
-	 * @see http://plasmasturm.org/log/444/
-	 *
-	 * @param string $cssSelector a CSS selector
-	 *
-	 * @return string the corresponding XPath selector
-	 */
-	private function translateCssToXpath($cssSelector)
-	{
-		$paddedSelector = ' ' . $cssSelector . ' ';
-		$lowercasePaddedSelector = preg_replace_callback(
-			'/\\s+\\w+\\s+/',
-			array( $this, 'translateCssToXpath_callback' ),
-			$paddedSelector
-		);
-
-		$trimmedLowercaseSelector = trim($lowercasePaddedSelector);
-		$xPathKey = md5($trimmedLowercaseSelector);
-		if (!isset($this->caches[self::CACHE_KEY_XPATH][$xPathKey])) {
-			$roughXpath = '//' . preg_replace(
-				array_keys($this->xPathRules),
-				$this->xPathRules,
-				$trimmedLowercaseSelector
-			);
-			$xPathWithIdAttributeMatchers = preg_replace_callback(
-				self::ID_ATTRIBUTE_MATCHER,
-				array($this, 'matchIdAttributes'),
-				$roughXpath
-			);
-			$xPathWithIdAttributeAndClassMatchers = preg_replace_callback(
-				self::CLASS_ATTRIBUTE_MATCHER,
-				array($this, 'matchClassAttributes'),
-				$xPathWithIdAttributeMatchers
-			);
-
-			// Advanced selectors are going to require a bit more advanced emogrification.
-			// When we required PHP 5.3, we could do this with closures.
-			$xPathWithIdAttributeAndClassMatchers = preg_replace_callback(
-				'/([^\\/]+):nth-child\\(\\s*(odd|even|[+\\-]?\\d|[+\\-]?\\d?n(\\s*[+\\-]\\s*\\d)?)\\s*\\)/i',
-				array($this, 'translateNthChild'),
-				$xPathWithIdAttributeAndClassMatchers
-			);
-			$finalXpath = preg_replace_callback(
-				'/([^\\/]+):nth-of-type\\(\s*(odd|even|[+\\-]?\\d|[+\\-]?\\d?n(\\s*[+\\-]\\s*\\d)?)\\s*\\)/i',
-				array($this, 'translateNthOfType'),
-				$xPathWithIdAttributeAndClassMatchers
-			);
-
-			$this->caches[self::CACHE_KEY_SELECTOR][$xPathKey] = $finalXpath;
-		}
-		return $this->caches[self::CACHE_KEY_SELECTOR][$xPathKey];
-	}
-
-	/**
-	 * @param string[] $match
-	 *
-	 * @return string
-	 */
-	private function matchIdAttributes(array $match)
-	{
-		return ($match[1] !== '' ? $match[1] : '*') . '[@id="' . $match[2] . '"]';
-	}
-
-	/**
-	 * @param string[] $match
-	 *
-	 * @return string
-	 */
-	private function matchClassAttributes(array $match)
-	{
-		return ($match[1] !== '' ? $match[1] : '*') . '[contains(concat(" ",@class," "),concat(" ","' .
-			implode(
-				'"," "))][contains(concat(" ",@class," "),concat(" ","',
-				explode('.', substr($match[2], 1))
-			) . '"," "))]';
-	}
-
-	/**
-	 * @param string[] $match
-	 *
-	 * @return string
-	 */
-	private function translateNthChild(array $match)
-	{
-		$parseResult = $this->parseNth($match);
-
-		if (isset($parseResult[self::MULTIPLIER])) {
-			if ($parseResult[self::MULTIPLIER] < 0) {
-				$parseResult[self::MULTIPLIER] = abs($parseResult[self::MULTIPLIER]);
-				$xPathExpression = sprintf(
-					'*[(last() - position()) mod %u = %u]/self::%s',
-					$parseResult[self::MULTIPLIER],
-					$parseResult[self::INDEX],
-					$match[1]
-				);
-			} else {
-				$xPathExpression = sprintf(
-					'*[position() mod %u = %u]/self::%s',
-					$parseResult[self::MULTIPLIER],
-					$parseResult[self::INDEX],
-					$match[1]
-				);
-			}
-		} else {
-			$xPathExpression = sprintf('*[%u]/self::%s', $parseResult[self::INDEX], $match[1]);
-		}
-
-		return $xPathExpression;
-	}
-
-	/**
-	 * @param string[] $match
-	 *
-	 * @return string
-	 */
-	private function translateNthOfType(array $match)
-	{
-		$parseResult = $this->parseNth($match);
-
-		if (isset($parseResult[self::MULTIPLIER])) {
-			if ($parseResult[self::MULTIPLIER] < 0) {
-				$parseResult[self::MULTIPLIER] = abs($parseResult[self::MULTIPLIER]);
-				$xPathExpression = sprintf(
-					'%s[(last() - position()) mod %u = %u]',
-					$match[1],
-					$parseResult[self::MULTIPLIER],
-					$parseResult[self::INDEX]
-				);
-			} else {
-				$xPathExpression = sprintf(
-					'%s[position() mod %u = %u]',
-					$match[1],
-					$parseResult[self::MULTIPLIER],
-					$parseResult[self::INDEX]
-				);
-			}
-		} else {
-			$xPathExpression = sprintf('%s[%u]', $match[1], $parseResult[self::INDEX]);
-		}
-
-		return $xPathExpression;
-	}
-
-	/**
-	 * @param string[] $match
-	 *
-	 * @return int[]
-	 */
-	private function parseNth(array $match)
-	{
-		if (in_array(strtolower($match[2]), array('even', 'odd'), true)) {
-			// we have "even" or "odd"
-			$index = strtolower($match[2]) === 'even' ? 0 : 1;
-			return array(self::MULTIPLIER => 2, self::INDEX => $index);
-		}
-		if (stripos($match[2], 'n') === false) {
-			// if there is a multiplier
-			$index = (int) str_replace(' ', '', $match[2]);
-			return array(self::INDEX => $index);
-		}
-
-		if (isset($match[3])) {
-			$multipleTerm = str_replace($match[3], '', $match[2]);
-			$index = (int) str_replace(' ', '', $match[3]);
-		} else {
-			$multipleTerm = $match[2];
-			$index = 0;
-		}
-
-		$multiplier = str_ireplace('n', '', $multipleTerm);
-
-		if ($multiplier === '') {
-			$multiplier = 1;
-		} elseif ($multiplier === '0') {
-			return array(self::INDEX => $index);
-		} else {
-			$multiplier = (int) $multiplier;
-		}
-
-		while ($index < 0) {
-			$index += abs($multiplier);
-		}
-
-		return array(self::MULTIPLIER => $multiplier, self::INDEX => $index);
-	}
-
-	/**
-	 * Parses a CSS declaration block into property name/value pairs.
-	 *
-	 * Example:
-	 *
-	 * The declaration block
-	 *
-	 *   "color: #000; font-weight: bold;"
-	 *
-	 * will be parsed into the following array:
-	 *
-	 *   "color" => "#000"
-	 *   "font-weight" => "bold"
-	 *
-	 * @param string $cssDeclarationsBlock the CSS declarations block without the curly braces, may be empty
-	 *
-	 * @return string[]
-	 *         the CSS declarations with the property names as array keys and the property values as array values
-	 */
-	private function parseCssDeclarationsBlock($cssDeclarationsBlock)
-	{
-		if (isset($this->caches[self::CACHE_KEY_CSS_DECLARATIONS_BLOCK][$cssDeclarationsBlock])) {
-			return $this->caches[self::CACHE_KEY_CSS_DECLARATIONS_BLOCK][$cssDeclarationsBlock];
-		}
-
-		$properties = array();
-		$declarations = preg_split('/;(?!base64|charset)/', $cssDeclarationsBlock);
-
-		foreach ($declarations as $declaration) {
-			$matches = array();
-			if (!preg_match('/^([A-Za-z\\-]+)\\s*:\\s*(.+)$/', trim($declaration), $matches)) {
-				continue;
-			}
-
-			$propertyName = strtolower($matches[1]);
-			$propertyValue = $matches[2];
-			$properties[$propertyName] = $propertyValue;
-		}
-		$this->caches[self::CACHE_KEY_CSS_DECLARATIONS_BLOCK][$cssDeclarationsBlock] = $properties;
-
-		return $properties;
-	}
-
-	/**
-	 * Find the nodes that are not to be emogrified.
-	 *
-	 * @param \DOMXPath $xPath
-	 *
-	 * @return \DOMElement[]
-	 */
-	private function getNodesToExclude(DOMXPath $xPath)
-	{
-		$excludedNodes = array();
-		foreach (array_keys($this->excludedSelectors) as $selectorToExclude) {
-			foreach ($xPath->query($this->translateCssToXpath($selectorToExclude)) as $node) {
-				$excludedNodes[] = $node;
-			}
-		}
-
-		return $excludedNodes;
-	}
-
-	/**
-	 * Handles invalid xPath expression warnings, generated by process() method,
-	 * during querying \DOMDocument and trigger \InvalidArgumentException
-	 * with invalid selector.
-	 *
-	 * @param int $type
-	 * @param string $message
-	 * @param string $file
-	 * @param int $line
-	 * @param array $context
-	 *
-	 * @return bool always false
-	 *
-	 * @throws \InvalidArgumentException
-	 */
-	public function handleXpathError($type, $message, $file, $line, array $context)
-	{
-		if ($type === E_WARNING && isset($context['cssRule']['selector'])) {
-			throw new InvalidArgumentException(
-				sprintf(
-					'%s in selector >> %s << in %s on line %s',
-					$message,
-					$context['cssRule']['selector'],
-					$file,
-					$line
-				)
-			);
-		}
-
-		// the normal error handling continues when handler return false
-		return false;
-	}
+    /**
+     * @var int
+     */
+    const CACHE_KEY_CSS = 0;
+
+    /**
+     * @var int
+     */
+    const CACHE_KEY_SELECTOR = 1;
+
+    /**
+     * @var int
+     */
+    const CACHE_KEY_XPATH = 2;
+
+    /**
+     * @var int
+     */
+    const CACHE_KEY_CSS_DECLARATIONS_BLOCK = 3;
+
+    /**
+     * @var int
+     */
+    const CACHE_KEY_COMBINED_STYLES = 4;
+
+    /**
+     * for calculating nth-of-type and nth-child selectors
+     *
+     * @var int
+     */
+    const INDEX = 0;
+
+    /**
+     * for calculating nth-of-type and nth-child selectors
+     *
+     * @var int
+     */
+    const MULTIPLIER = 1;
+
+    /**
+     * @var string
+     */
+    const ID_ATTRIBUTE_MATCHER = '/(\\w+)?\\#([\\w\\-]+)/';
+
+    /**
+     * @var string
+     */
+    const CLASS_ATTRIBUTE_MATCHER = '/(\\w+|[\\*\\]])?((\\.[\\w\\-]+)+)/';
+
+    /**
+     * @var string
+     */
+    const CONTENT_TYPE_META_TAG = '<meta http-equiv="Content-Type" content="text/html; charset=utf-8">';
+
+    /**
+     * @var string
+     */
+    const DEFAULT_DOCUMENT_TYPE = '<!DOCTYPE html>';
+
+    /**
+     * @var string
+     */
+    private $html = '';
+
+    /**
+     * @var string
+     */
+    private $css = '';
+
+    /**
+     * @var bool[]
+     */
+    private $excludedSelectors = [];
+
+    /**
+     * @var string[]
+     */
+    private $unprocessableHtmlTags = ['wbr'];
+
+    /**
+     * @var bool[]
+     */
+    private $allowedMediaTypes = ['all' => true, 'screen' => true, 'print' => true];
+
+    /**
+     * @var mixed[]
+     */
+    private $caches = [
+        self::CACHE_KEY_CSS => [],
+        self::CACHE_KEY_SELECTOR => [],
+        self::CACHE_KEY_XPATH => [],
+        self::CACHE_KEY_CSS_DECLARATIONS_BLOCK => [],
+        self::CACHE_KEY_COMBINED_STYLES => [],
+    ];
+
+    /**
+     * the visited nodes with the XPath paths as array keys
+     *
+     * @var \DOMElement[]
+     */
+    private $visitedNodes = [];
+
+    /**
+     * the styles to apply to the nodes with the XPath paths as array keys for the outer array
+     * and the attribute names/values as key/value pairs for the inner array
+     *
+     * @var string[][]
+     */
+    private $styleAttributesForNodes = [];
+
+    /**
+     * Determines whether the "style" attributes of tags in the the HTML passed to this class should be preserved.
+     * If set to false, the value of the style attributes will be discarded.
+     *
+     * @var bool
+     */
+    private $isInlineStyleAttributesParsingEnabled = true;
+
+    /**
+     * Determines whether the <style> blocks in the HTML passed to this class should be parsed.
+     *
+     * If set to true, the <style> blocks will be removed from the HTML and their contents will be applied to the HTML
+     * via inline styles.
+     *
+     * If set to false, the <style> blocks will be left as they are in the HTML.
+     *
+     * @var bool
+     */
+    private $isStyleBlocksParsingEnabled = true;
+
+    /**
+     * Determines whether elements with the `display: none` property are
+     * removed from the DOM.
+     *
+     * @var bool
+     */
+    private $shouldKeepInvisibleNodes = true;
+
+    /**
+     * @var string[]
+     */
+    private $xPathRules = [
+        // attribute presence
+        '/^\\[(\\w+|\\w+\\=[\'"]?\\w+[\'"]?)\\]/' => '*[@\\1]',
+        // type and attribute exact value
+        '/(\\w)\\[(\\w+)\\=[\'"]?([\\w\\s]+)[\'"]?\\]/' => '\\1[@\\2="\\3"]',
+        // type and attribute value with ~ (one word within a whitespace-separated list of words)
+        '/([\\w\\*]+)\\[(\\w+)[\\s]*\\~\\=[\\s]*[\'"]?([\\w-_\\/]+)[\'"]?\\]/'
+        => '\\1[contains(concat(" ", @\\2, " "), concat(" ", "\\3", " "))]',
+        // type and attribute value with | (either exact value match or prefix followed by a hyphen)
+        '/([\\w\\*]+)\\[(\\w+)[\\s]*\\|\\=[\\s]*[\'"]?([\\w-_\\s\\/]+)[\'"]?\\]/'
+        => '\\1[@\\2="\\3" or starts-with(@\\2, concat("\\3", "-"))]',
+        // type and attribute value with ^ (prefix match)
+        '/([\\w\\*]+)\\[(\\w+)[\\s]*\\^\\=[\\s]*[\'"]?([\\w-_\\/]+)[\'"]?\\]/' => '\\1[starts-with(@\\2, "\\3")]',
+        // type and attribute value with * (substring match)
+        '/([\\w\\*]+)\\[(\\w+)[\\s]*\\*\\=[\\s]*[\'"]?([\\w-_\\s\\/:;]+)[\'"]?\\]/' => '\\1[contains(@\\2, "\\3")]',
+        // adjacent sibling
+        '/\\s+\\+\\s+/' => '/following-sibling::*[1]/self::',
+        // child
+        '/\\s*>\\s*/' => '/',
+        // descendant
+        '/\\s+(?=.*[^\\]]{1}$)/' => '//',
+        // type and :first-child
+        '/([^\\/]+):first-child/i' => '*[1]/self::\\1',
+        // type and :last-child
+        '/([^\\/]+):last-child/i' => '*[last()]/self::\\1',
+
+        // The following matcher will break things if it is placed before the adjacent matcher.
+        // So one of the matchers matches either too much or not enough.
+        // type and attribute value with $ (suffix match)
+        '/([\\w\\*]+)\\[(\\w+)[\\s]*\\$\\=[\\s]*[\'"]?([\\w-_\\s\\/]+)[\'"]?\\]/'
+        => '\\1[substring(@\\2, string-length(@\\2) - string-length("\\3") + 1) = "\\3"]',
+    ];
+
+    /**
+     * Determines whether CSS styles that have an equivalent HTML attribute
+     * should be mapped and attached to those elements.
+     *
+     * @var bool
+     */
+    private $shouldMapCssToHtml = false;
+
+    /**
+     * This multi-level array contains simple mappings of CSS properties to
+     * HTML attributes. If a mapping only applies to certain HTML nodes or
+     * only for certain values, the mapping is an object with a whitelist
+     * of nodes and values.
+     *
+     * @var mixed[][]
+     */
+    private $cssToHtmlMap = [
+        'background-color' => [
+            'attribute' => 'bgcolor',
+        ],
+        'text-align' => [
+            'attribute' => 'align',
+            'nodes' => ['p', 'div', 'td'],
+            'values' => ['left', 'right', 'center', 'justify'],
+        ],
+        'float' => [
+            'attribute' => 'align',
+            'nodes' => ['table', 'img'],
+            'values' => ['left', 'right'],
+        ],
+        'border-spacing' => [
+            'attribute' => 'cellspacing',
+            'nodes' => ['table'],
+        ],
+    ];
+
+    /**
+     * Emogrifier will throw Exceptions when it encounters an error instead of silently ignoring them.
+     *
+     * @var bool
+     */
+    private $debug = false;
+
+    /**
+     * The constructor.
+     *
+     * @param string $html the HTML to emogrify, must be UTF-8-encoded
+     * @param string $css the CSS to merge, must be UTF-8-encoded
+     */
+    public function __construct($html = '', $css = '')
+    {
+        $this->setHtml($html);
+        $this->setCss($css);
+    }
+
+    /**
+     * The destructor.
+     */
+    public function __destruct()
+    {
+        $this->purgeVisitedNodes();
+    }
+
+    /**
+     * Sets the HTML to emogrify.
+     *
+     * @param string $html the HTML to emogrify, must be UTF-8-encoded
+     *
+     * @return void
+     */
+    public function setHtml($html)
+    {
+        $this->html = $html;
+    }
+
+    /**
+     * Sets the CSS to merge with the HTML.
+     *
+     * @param string $css the CSS to merge, must be UTF-8-encoded
+     *
+     * @return void
+     */
+    public function setCss($css)
+    {
+        $this->css = $css;
+    }
+
+    /**
+     * Applies $this->css to $this->html and returns the HTML with the CSS
+     * applied.
+     *
+     * This method places the CSS inline.
+     *
+     * @return string
+     *
+     * @throws \BadMethodCallException
+     */
+    public function emogrify()
+    {
+        return $this->createAndProcessXmlDocument()->saveHTML();
+    }
+
+    /**
+     * Applies $this->css to $this->html and returns only the HTML content
+     * within the <body> tag.
+     *
+     * This method places the CSS inline.
+     *
+     * @return string
+     *
+     * @throws \BadMethodCallException
+     */
+    public function emogrifyBodyContent()
+    {
+        $xmlDocument = $this->createAndProcessXmlDocument();
+        $bodyNodeHtml = $xmlDocument->saveHTML($this->getBodyElement($xmlDocument));
+
+        return str_replace(['<body>', '</body>'], '', $bodyNodeHtml);
+    }
+
+    /**
+     * Creates an XML document from $this->html and emogrifies ist.
+     *
+     * @return \DOMDocument
+     *
+     * @throws \BadMethodCallException
+     */
+    private function createAndProcessXmlDocument()
+    {
+        if ($this->html === '') {
+            throw new \BadMethodCallException('Please set some HTML first.', 1390393096);
+        }
+
+        $xmlDocument = $this->createRawXmlDocument();
+        $this->ensureExistenceOfBodyElement($xmlDocument);
+        $this->process($xmlDocument);
+
+        return $xmlDocument;
+    }
+
+    /**
+     * Applies $this->css to $xmlDocument.
+     *
+     * This method places the CSS inline.
+     *
+     * @param \DOMDocument $xmlDocument
+     *
+     * @return void
+     *
+     * @throws \InvalidArgumentException
+     */
+    protected function process(\DOMDocument $xmlDocument)
+    {
+        $xPath = new \DOMXPath($xmlDocument);
+        $this->clearAllCaches();
+        $this->purgeVisitedNodes();
+        set_error_handler([$this, 'handleXpathQueryWarnings'], E_WARNING);
+
+        $this->normalizeStyleAttributesOfAllNodes($xPath);
+
+        // grab any existing style blocks from the html and append them to the existing CSS
+        // (these blocks should be appended so as to have precedence over conflicting styles in the existing CSS)
+        $allCss = $this->css;
+        if ($this->isStyleBlocksParsingEnabled) {
+            $allCss .= $this->getCssFromAllStyleNodes($xPath);
+        }
+
+        $cssParts = $this->splitCssAndMediaQuery($allCss);
+        $excludedNodes = $this->getNodesToExclude($xPath);
+        $cssRules = $this->parseCssRules($cssParts['css']);
+        foreach ($cssRules as $cssRule) {
+            // There's no real way to test "PHP Warning" output generated by the following XPath query unless PHPUnit
+            // converts it to an exception. Unfortunately, this would only apply to tests and not work for production
+            // executions, which can still flood logs/output unnecessarily. Instead, Emogrifier's error handler should
+            // always throw an exception and it must be caught here and only rethrown if in debug mode.
+            try {
+                // \DOMXPath::query will always return a DOMNodeList or an exception when errors are caught.
+                $nodesMatchingCssSelectors = $xPath->query($this->translateCssToXpath($cssRule['selector']));
+            } catch (\InvalidArgumentException $e) {
+                if ($this->debug) {
+                    throw $e;
+                }
+                continue;
+            }
+
+            /** @var \DOMElement $node */
+            foreach ($nodesMatchingCssSelectors as $node) {
+                if (in_array($node, $excludedNodes, true)) {
+                    continue;
+                }
+                // if it has a style attribute, get it, process it, and append (overwrite) new stuff
+                if ($node->hasAttribute('style')) {
+                    // break it up into an associative array
+                    $oldStyleDeclarations = $this->parseCssDeclarationsBlock($node->getAttribute('style'));
+                } else {
+                    $oldStyleDeclarations = [];
+                }
+                $newStyleDeclarations = $this->parseCssDeclarationsBlock($cssRule['declarationsBlock']);
+                $node->setAttribute(
+                    'style',
+                    $this->generateStyleStringFromDeclarationsArrays($oldStyleDeclarations, $newStyleDeclarations)
+                );
+            }
+        }
+
+        if ($this->isInlineStyleAttributesParsingEnabled) {
+            $this->fillStyleAttributesWithMergedStyles();
+        }
+
+        if ($this->shouldMapCssToHtml) {
+            $this->mapAllInlineStylesToHtmlAttributes($xPath);
+        }
+
+        if ($this->shouldKeepInvisibleNodes) {
+            $this->removeInvisibleNodes($xPath);
+        }
+
+        $this->removeImportantAnnotationFromAllInlineStyles($xPath);
+
+        $this->copyCssWithMediaToStyleNode($xmlDocument, $xPath, $cssParts['media']);
+
+        restore_error_handler();
+    }
+
+    /**
+     * Searches for all nodes with a style attribute, transforms the CSS found
+     * to HTML attributes and adds those attributes to each node.
+     *
+     * @param \DOMXPath $xPath
+     *
+     * @return void
+     */
+    private function mapAllInlineStylesToHtmlAttributes(\DOMXPath $xPath)
+    {
+        /** @var \DOMElement $node */
+        foreach ($this->getAllNodesWithStyleAttribute($xPath) as $node) {
+            $inlineStyleDeclarations = $this->parseCssDeclarationsBlock($node->getAttribute('style'));
+            $this->mapCssToHtmlAttributes($inlineStyleDeclarations, $node);
+        }
+    }
+
+    /**
+     * Searches for all nodes with a style attribute and removes the "!important" annotations out of
+     * the inline style declarations, eventually by rearranging declarations.
+     *
+     * @param \DOMXPath $xPath
+     *
+     * @return void
+     */
+    private function removeImportantAnnotationFromAllInlineStyles(\DOMXPath $xPath)
+    {
+        foreach ($this->getAllNodesWithStyleAttribute($xPath) as $node) {
+            $this->removeImportantAnnotationFromNodeInlineStyle($node);
+        }
+    }
+
+    /**
+     * Removes the "!important" annotations out of the inline style declarations,
+     * eventually by rearranging declarations.
+     * Rearranging needed when !important shorthand properties are followed by some of their
+     * not !important expanded-version properties.
+     * For example "font: 12px serif !important; font-size: 13px;" must be reordered
+     * to "font-size: 13px; font: 12px serif;" in order to remain correct.
+     *
+     * @param \DOMElement $node
+     *
+     * @return void
+     */
+    private function removeImportantAnnotationFromNodeInlineStyle(\DOMElement $node)
+    {
+        $inlineStyleDeclarations = $this->parseCssDeclarationsBlock($node->getAttribute('style'));
+        $regularStyleDeclarations = [];
+        $importantStyleDeclarations = [];
+        foreach ($inlineStyleDeclarations as $property => $value) {
+            if ($this->attributeValueIsImportant($value)) {
+                $importantStyleDeclarations[$property] = trim(str_replace('!important', '', $value));
+            } else {
+                $regularStyleDeclarations[$property] = $value;
+            }
+        }
+        $inlineStyleDeclarationsInNewOrder = array_merge(
+            $regularStyleDeclarations,
+            $importantStyleDeclarations
+        );
+        $node->setAttribute(
+            'style',
+            $this->generateStyleStringFromSingleDeclarationsArray($inlineStyleDeclarationsInNewOrder)
+        );
+    }
+
+    /**
+     * Returns a list with all DOM nodes that have a style attribute.
+     *
+     * @param \DOMXPath $xPath
+     *
+     * @return \DOMNodeList
+     */
+    private function getAllNodesWithStyleAttribute(\DOMXPath $xPath)
+    {
+        return $xPath->query('//*[@style]');
+    }
+
+    /**
+     * Applies $styles to $node.
+     *
+     * This method maps CSS styles to HTML attributes and adds those to the
+     * node.
+     *
+     * @param string[] $styles the new CSS styles taken from the global styles to be applied to this node
+     * @param \DOMElement $node node to apply styles to
+     *
+     * @return void
+     */
+    private function mapCssToHtmlAttributes(array $styles, \DOMElement $node)
+    {
+        foreach ($styles as $property => $value) {
+            // Strip !important indicator
+            $value = trim(str_replace('!important', '', $value));
+            $this->mapCssToHtmlAttribute($property, $value, $node);
+        }
+    }
+
+    /**
+     * Tries to apply the CSS style to $node as an attribute.
+     *
+     * This method maps a CSS rule to HTML attributes and adds those to the node.
+     *
+     * @param string $property the name of the CSS property to map
+     * @param string $value the value of the style rule to map
+     * @param \DOMElement $node node to apply styles to
+     *
+     * @return void
+     */
+    private function mapCssToHtmlAttribute($property, $value, \DOMElement $node)
+    {
+        if (!$this->mapSimpleCssProperty($property, $value, $node)) {
+            $this->mapComplexCssProperty($property, $value, $node);
+        }
+    }
+
+    /**
+     * Looks up the CSS property in the mapping table and maps it if it matches the conditions.
+     *
+     * @param string $property the name of the CSS property to map
+     * @param string $value the value of the style rule to map
+     * @param \DOMElement $node node to apply styles to
+     *
+     * @return bool true if the property cab be mapped using the simple mapping table
+     */
+    private function mapSimpleCssProperty($property, $value, \DOMElement $node)
+    {
+        if (!isset($this->cssToHtmlMap[$property])) {
+            return false;
+        }
+
+        $mapping = $this->cssToHtmlMap[$property];
+        $nodesMatch = !isset($mapping['nodes']) || in_array($node->nodeName, $mapping['nodes'], true);
+        $valuesMatch = !isset($mapping['values']) || in_array($value, $mapping['values'], true);
+        if (!$nodesMatch || !$valuesMatch) {
+            return false;
+        }
+
+        $node->setAttribute($mapping['attribute'], $value);
+
+        return true;
+    }
+
+    /**
+     * Maps CSS properties that need special transformation to an HTML attribute.
+     *
+     * @param string $property the name of the CSS property to map
+     * @param string $value the value of the style rule to map
+     * @param \DOMElement $node node to apply styles to
+     *
+     * @return void
+     */
+    private function mapComplexCssProperty($property, $value, \DOMElement $node)
+    {
+        $nodeName = $node->nodeName;
+        $isTable = $nodeName === 'table';
+        $isImage = $nodeName === 'img';
+        $isTableOrImage = $isTable || $isImage;
+
+        switch ($property) {
+            case 'background':
+                // Parse out the color, if any
+                $styles = explode(' ', $value);
+                $first = $styles[0];
+                if (!is_numeric($first[0]) && strpos($first, 'url') !== 0) {
+                    // This is not a position or image, assume it's a color
+                    $node->setAttribute('bgcolor', $first);
+                }
+                break;
+            case 'width':
+                // intentional fall-through
+            case 'height':
+                // Only parse values in px and %, but not values like "auto".
+                if (preg_match('/^\d+(px|%)$/', $value)) {
+                    // Remove 'px'. This regex only conserves numbers and %
+                    $number = preg_replace('/[^0-9.%]/', '', $value);
+                    $node->setAttribute($property, $number);
+                }
+                break;
+            case 'margin':
+                if ($isTableOrImage) {
+                    $margins = $this->parseCssShorthandValue($value);
+                    if ($margins['left'] === 'auto' && $margins['right'] === 'auto') {
+                        $node->setAttribute('align', 'center');
+                    }
+                }
+                break;
+            case 'border':
+                if ($isTableOrImage) {
+                    if ($value === 'none' || $value === '0') {
+                        $node->setAttribute('border', '0');
+                    }
+                }
+                break;
+            default:
+        }
+    }
+
+    /**
+     * Parses a shorthand CSS value and splits it into individual values
+     *
+     * @param string $value a string of CSS value with 1, 2, 3 or 4 sizes
+     *                      For example: padding: 0 auto;
+     *                      '0 auto' is split into top: 0, left: auto, bottom: 0,
+     *                      right: auto.
+     *
+     * @return string[] an array of values for top, right, bottom and left (using these as associative array keys)
+     */
+    private function parseCssShorthandValue($value)
+    {
+        $values = preg_split('/\\s+/', $value);
+
+        $css = [];
+        $css['top'] = $values[0];
+        $css['right'] = (count($values) > 1) ? $values[1] : $css['top'];
+        $css['bottom'] = (count($values) > 2) ? $values[2] : $css['top'];
+        $css['left'] = (count($values) > 3) ? $values[3] : $css['right'];
+
+        return $css;
+    }
+
+    /**
+     * Extracts and parses the individual rules from a CSS string.
+     *
+     * @param string $css a string of raw CSS code
+     *
+     * @return string[][] an array of string sub-arrays with the keys
+     *         "selector" (the CSS selector(s), e.g., "*" or "h1"),
+     *         "declarationsBLock" (the semicolon-separated CSS declarations for that selector(s),
+     *         e.g., "color: red; height: 4px;"),
+     *         and "line" (the line number e.g. 42)
+     */
+    private function parseCssRules($css)
+    {
+        $cssKey = md5($css);
+        if (!isset($this->caches[self::CACHE_KEY_CSS][$cssKey])) {
+            // process the CSS file for selectors and definitions
+            preg_match_all('/(?:^|[\\s^{}]*)([^{]+){([^}]*)}/mi', $css, $matches, PREG_SET_ORDER);
+
+            $cssRules = [];
+            /** @var string[][] $matches */
+            /** @var string[] $cssRule */
+            foreach ($matches as $key => $cssRule) {
+                $cssDeclaration = trim($cssRule[2]);
+                if ($cssDeclaration === '') {
+                    continue;
+                }
+
+                $selectors = explode(',', $cssRule[1]);
+                foreach ($selectors as $selector) {
+                    // don't process pseudo-elements and behavioral (dynamic) pseudo-classes;
+                    // only allow structural pseudo-classes
+                    $hasPseudoElement = strpos($selector, '::') !== false;
+                    $hasAnyPseudoClass = (bool)preg_match('/:[a-zA-Z]/', $selector);
+                    $hasSupportedPseudoClass = (bool)preg_match(
+                        '/:(\\S+\\-(child|type\\()|not\\([[:ascii:]]*\\))/i',
+                        $selector
+                    );
+                    if ($hasPseudoElement || ($hasAnyPseudoClass && !$hasSupportedPseudoClass)) {
+                        continue;
+                    }
+
+                    $cssRules[] = [
+                        'selector' => trim($selector),
+                        'declarationsBlock' => $cssDeclaration,
+                        // keep track of where it appears in the file, since order is important
+                        'line' => $key,
+                    ];
+                }
+            }
+
+            usort($cssRules, [$this, 'sortBySelectorPrecedence']);
+
+            $this->caches[self::CACHE_KEY_CSS][$cssKey] = $cssRules;
+        }
+
+        return $this->caches[self::CACHE_KEY_CSS][$cssKey];
+    }
+
+    /**
+     * Disables the parsing of inline styles.
+     *
+     * @return void
+     */
+    public function disableInlineStyleAttributesParsing()
+    {
+        $this->isInlineStyleAttributesParsingEnabled = false;
+    }
+
+    /**
+     * Disables the parsing of <style> blocks.
+     *
+     * @return void
+     */
+    public function disableStyleBlocksParsing()
+    {
+        $this->isStyleBlocksParsingEnabled = false;
+    }
+
+    /**
+     * Disables the removal of elements with `display: none` properties.
+     *
+     * @return void
+     */
+    public function disableInvisibleNodeRemoval()
+    {
+        $this->shouldKeepInvisibleNodes = false;
+    }
+
+    /**
+     * Enables the attachment/override of HTML attributes for which a
+     * corresponding CSS property has been set.
+     *
+     * @return void
+     */
+    public function enableCssToHtmlMapping()
+    {
+        $this->shouldMapCssToHtml = true;
+    }
+
+    /**
+     * Clears all caches.
+     *
+     * @return void
+     */
+    private function clearAllCaches()
+    {
+        $this->clearCache(self::CACHE_KEY_CSS);
+        $this->clearCache(self::CACHE_KEY_SELECTOR);
+        $this->clearCache(self::CACHE_KEY_XPATH);
+        $this->clearCache(self::CACHE_KEY_CSS_DECLARATIONS_BLOCK);
+        $this->clearCache(self::CACHE_KEY_COMBINED_STYLES);
+    }
+
+    /**
+     * Clears a single cache by key.
+     *
+     * @param int $key the cache key, must be CACHE_KEY_CSS, CACHE_KEY_SELECTOR, CACHE_KEY_XPATH
+     *                 or CACHE_KEY_CSS_DECLARATION_BLOCK
+     *
+     * @return void
+     *
+     * @throws \InvalidArgumentException
+     */
+    private function clearCache($key)
+    {
+        $allowedCacheKeys = [
+            self::CACHE_KEY_CSS,
+            self::CACHE_KEY_SELECTOR,
+            self::CACHE_KEY_XPATH,
+            self::CACHE_KEY_CSS_DECLARATIONS_BLOCK,
+            self::CACHE_KEY_COMBINED_STYLES,
+        ];
+        if (!in_array($key, $allowedCacheKeys, true)) {
+            throw new \InvalidArgumentException('Invalid cache key: ' . $key, 1391822035);
+        }
+
+        $this->caches[$key] = [];
+    }
+
+    /**
+     * Purges the visited nodes.
+     *
+     * @return void
+     */
+    private function purgeVisitedNodes()
+    {
+        $this->visitedNodes = [];
+        $this->styleAttributesForNodes = [];
+    }
+
+    /**
+     * Marks a tag for removal.
+     *
+     * There are some HTML tags that DOMDocument cannot process, and it will throw an error if it encounters them.
+     * In particular, DOMDocument will complain if you try to use HTML5 tags in an XHTML document.
+     *
+     * Note: The tags will not be removed if they have any content.
+     *
+     * @param string $tagName the tag name, e.g., "p"
+     *
+     * @return void
+     */
+    public function addUnprocessableHtmlTag($tagName)
+    {
+        $this->unprocessableHtmlTags[] = $tagName;
+    }
+
+    /**
+     * Drops a tag from the removal list.
+     *
+     * @param string $tagName the tag name, e.g., "p"
+     *
+     * @return void
+     */
+    public function removeUnprocessableHtmlTag($tagName)
+    {
+        $key = array_search($tagName, $this->unprocessableHtmlTags, true);
+        if ($key !== false) {
+            unset($this->unprocessableHtmlTags[$key]);
+        }
+    }
+
+    /**
+     * Marks a media query type to keep.
+     *
+     * @param string $mediaName the media type name, e.g., "braille"
+     *
+     * @return void
+     */
+    public function addAllowedMediaType($mediaName)
+    {
+        $this->allowedMediaTypes[$mediaName] = true;
+    }
+
+    /**
+     * Drops a media query type from the allowed list.
+     *
+     * @param string $mediaName the tag name, e.g., "braille"
+     *
+     * @return void
+     */
+    public function removeAllowedMediaType($mediaName)
+    {
+        if (isset($this->allowedMediaTypes[$mediaName])) {
+            unset($this->allowedMediaTypes[$mediaName]);
+        }
+    }
+
+    /**
+     * Adds a selector to exclude nodes from emogrification.
+     *
+     * Any nodes that match the selector will not have their style altered.
+     *
+     * @param string $selector the selector to exclude, e.g., ".editor"
+     *
+     * @return void
+     */
+    public function addExcludedSelector($selector)
+    {
+        $this->excludedSelectors[$selector] = true;
+    }
+
+    /**
+     * No longer excludes the nodes matching this selector from emogrification.
+     *
+     * @param string $selector the selector to no longer exclude, e.g., ".editor"
+     *
+     * @return void
+     */
+    public function removeExcludedSelector($selector)
+    {
+        if (isset($this->excludedSelectors[$selector])) {
+            unset($this->excludedSelectors[$selector]);
+        }
+    }
+
+    /**
+     * This removes styles from your email that contain display:none.
+     * We need to look for display:none, but we need to do a case-insensitive search. Since DOMDocument only
+     * supports XPath 1.0, lower-case() isn't available to us. We've thus far only set attributes to lowercase,
+     * not attribute values. Consequently, we need to translate() the letters that would be in 'NONE' ("NOE")
+     * to lowercase.
+     *
+     * @param \DOMXPath $xPath
+     *
+     * @return void
+     */
+    private function removeInvisibleNodes(\DOMXPath $xPath)
+    {
+        $nodesWithStyleDisplayNone = $xPath->query(
+            '//*[contains(translate(translate(@style," ",""),"NOE","noe"),"display:none")]'
+        );
+        if ($nodesWithStyleDisplayNone->length === 0) {
+            return;
+        }
+
+        // The checks on parentNode and is_callable below ensure that if we've deleted the parent node,
+        // we don't try to call removeChild on a nonexistent child node
+        /** @var \DOMNode $node */
+        foreach ($nodesWithStyleDisplayNone as $node) {
+            if ($node->parentNode && is_callable([$node->parentNode, 'removeChild'])) {
+                $node->parentNode->removeChild($node);
+            }
+        }
+    }
+
+    /**
+     * Parses the document and normalizes all existing CSS attributes.
+     * This changes 'DISPLAY: none' to 'display: none'.
+     * We wouldn't have to do this if DOMXPath supported XPath 2.0.
+     * Also stores a reference of nodes with existing inline styles so we don't overwrite them.
+     *
+     * @param \DOMXPath $xPath
+     *
+     * @return void
+     */
+    private function normalizeStyleAttributesOfAllNodes(\DOMXPath $xPath)
+    {
+        /** @var \DOMElement $node */
+        foreach ($this->getAllNodesWithStyleAttribute($xPath) as $node) {
+            if ($this->isInlineStyleAttributesParsingEnabled) {
+                $this->normalizeStyleAttributes($node);
+            }
+            // Remove style attribute in every case, so we can add them back (if inline style attributes
+            // parsing is enabled) to the end of the style list, thus keeping the right priority of CSS rules;
+            // else original inline style rules may remain at the beginning of the final inline style definition
+            // of a node, which may give not the desired results
+            $node->removeAttribute('style');
+        }
+    }
+
+    /**
+     * Normalizes the value of the "style" attribute and saves it.
+     *
+     * @param \DOMElement $node
+     *
+     * @return void
+     */
+    private function normalizeStyleAttributes(\DOMElement $node)
+    {
+        $normalizedOriginalStyle = preg_replace_callback(
+            '/[A-z\\-]+(?=\\:)/S',
+            function (array $m) {
+                return strtolower($m[0]);
+            },
+            $node->getAttribute('style')
+        );
+
+        // in order to not overwrite existing style attributes in the HTML, we
+        // have to save the original HTML styles
+        $nodePath = $node->getNodePath();
+        if (!isset($this->styleAttributesForNodes[$nodePath])) {
+            $this->styleAttributesForNodes[$nodePath] = $this->parseCssDeclarationsBlock($normalizedOriginalStyle);
+            $this->visitedNodes[$nodePath] = $node;
+        }
+
+        $node->setAttribute('style', $normalizedOriginalStyle);
+    }
+
+    /**
+     * Merges styles from styles attributes and style nodes and applies them to the attribute nodes
+     *
+     * @return void
+     */
+    private function fillStyleAttributesWithMergedStyles()
+    {
+        foreach ($this->styleAttributesForNodes as $nodePath => $styleAttributesForNode) {
+            $node = $this->visitedNodes[$nodePath];
+            $currentStyleAttributes = $this->parseCssDeclarationsBlock($node->getAttribute('style'));
+            $node->setAttribute(
+                'style',
+                $this->generateStyleStringFromDeclarationsArrays(
+                    $currentStyleAttributes,
+                    $styleAttributesForNode
+                )
+            );
+        }
+    }
+
+    /**
+     * This method merges old or existing name/value array with new name/value array
+     * and then generates a string of the combined style suitable for placing inline.
+     * This becomes the single point for CSS string generation allowing for consistent
+     * CSS output no matter where the CSS originally came from.
+     *
+     * @param string[] $oldStyles
+     * @param string[] $newStyles
+     *
+     * @return string
+     */
+    private function generateStyleStringFromDeclarationsArrays(array $oldStyles, array $newStyles)
+    {
+        $combinedStyles = array_merge($oldStyles, $newStyles);
+        $cacheKey = serialize($combinedStyles);
+        if (isset($this->caches[self::CACHE_KEY_COMBINED_STYLES][$cacheKey])) {
+            return $this->caches[self::CACHE_KEY_COMBINED_STYLES][$cacheKey];
+        }
+
+        foreach ($oldStyles as $attributeName => $attributeValue) {
+            if (!isset($newStyles[$attributeName])) {
+                continue;
+            }
+
+            $newAttributeValue = $newStyles[$attributeName];
+            if ($this->attributeValueIsImportant($attributeValue)
+                && !$this->attributeValueIsImportant($newAttributeValue)
+            ) {
+                $combinedStyles[$attributeName] = $attributeValue;
+            }
+        }
+
+        $style = '';
+        foreach ($combinedStyles as $attributeName => $attributeValue) {
+            $style .= strtolower(trim($attributeName)) . ': ' . trim($attributeValue) . '; ';
+        }
+        $trimmedStyle = rtrim($style);
+
+        $this->caches[self::CACHE_KEY_COMBINED_STYLES][$cacheKey] = $trimmedStyle;
+
+        return $trimmedStyle;
+    }
+
+    /**
+     * Generates a CSS style string suitable to be used inline from the $styleDeclarations property => value array.
+     *
+     * @param string[] $styleDeclarations
+     *
+     * @return string
+     */
+    private function generateStyleStringFromSingleDeclarationsArray(array $styleDeclarations)
+    {
+        return $this->generateStyleStringFromDeclarationsArrays([], $styleDeclarations);
+    }
+
+    /**
+     * Checks whether $attributeValue is marked as !important.
+     *
+     * @param string $attributeValue
+     *
+     * @return bool
+     */
+    private function attributeValueIsImportant($attributeValue)
+    {
+        return strtolower(substr(trim($attributeValue), -10)) === '!important';
+    }
+
+    /**
+     * Applies $css to $xmlDocument, limited to the media queries that actually apply to the document.
+     *
+     * @param \DOMDocument $xmlDocument the document to match against
+     * @param \DOMXPath $xPath
+     * @param string $css a string of CSS
+     *
+     * @return void
+     */
+    private function copyCssWithMediaToStyleNode(\DOMDocument $xmlDocument, \DOMXPath $xPath, $css)
+    {
+        if ($css === '') {
+            return;
+        }
+
+        $mediaQueriesRelevantForDocument = [];
+
+        foreach ($this->extractMediaQueriesFromCss($css) as $mediaQuery) {
+            foreach ($this->parseCssRules($mediaQuery['css']) as $selector) {
+                if ($this->existsMatchForCssSelector($xPath, $selector['selector'])) {
+                    $mediaQueriesRelevantForDocument[] = $mediaQuery['query'];
+                    break;
+                }
+            }
+        }
+
+        $this->addStyleElementToDocument($xmlDocument, implode($mediaQueriesRelevantForDocument));
+    }
+
+    /**
+     * Extracts the media queries from $css while skipping empty media queries.
+     *
+     * @param string $css
+     *
+     * @return string[][] numeric array with string sub-arrays with the keys "css" and "query"
+     */
+    private function extractMediaQueriesFromCss($css)
+    {
+        preg_match_all('/@media\\b[^{]*({((?:[^{}]+|(?1))*)})/', $css, $rawMediaQueries, PREG_SET_ORDER);
+        $parsedQueries = [];
+
+        /** @var string[][] $rawMediaQueries */
+        foreach ($rawMediaQueries as $mediaQuery) {
+            if ($mediaQuery[2] !== '') {
+                $parsedQueries[] = [
+                    'css' => $mediaQuery[2],
+                    'query' => $mediaQuery[0],
+                ];
+            }
+        }
+
+        return $parsedQueries;
+    }
+
+    /**
+     * Checks whether there is at least one matching element for $cssSelector.
+     * When not in debug mode, it returns true also for invalid selectors (because they may be valid,
+     * just not implemented/recognized yet by Emogrifier).
+     *
+     * @param \DOMXPath $xPath
+     * @param string $cssSelector
+     *
+     * @return bool
+     *
+     * @throws \InvalidArgumentException
+     */
+    private function existsMatchForCssSelector(\DOMXPath $xPath, $cssSelector)
+    {
+        try {
+            $nodesMatchingSelector = $xPath->query($this->translateCssToXpath($cssSelector));
+        } catch (\InvalidArgumentException $e) {
+            if ($this->debug) {
+                throw $e;
+            }
+            return true;
+        }
+
+        return $nodesMatchingSelector !== false && $nodesMatchingSelector->length !== 0;
+    }
+
+    /**
+     * Returns CSS content.
+     *
+     * @param \DOMXPath $xPath
+     *
+     * @return string
+     */
+    private function getCssFromAllStyleNodes(\DOMXPath $xPath)
+    {
+        $styleNodes = $xPath->query('//style');
+
+        if ($styleNodes === false) {
+            return '';
+        }
+
+        $css = '';
+        /** @var \DOMNode $styleNode */
+        foreach ($styleNodes as $styleNode) {
+            $css .= "\n\n" . $styleNode->nodeValue;
+            $styleNode->parentNode->removeChild($styleNode);
+        }
+
+        return $css;
+    }
+
+    /**
+     * Adds a style element with $css to $document.
+     *
+     * This method is protected to allow overriding.
+     *
+     * @see https://github.com/jjriv/emogrifier/issues/103
+     *
+     * @param \DOMDocument $document
+     * @param string $css
+     *
+     * @return void
+     */
+    protected function addStyleElementToDocument(\DOMDocument $document, $css)
+    {
+        $styleElement = $document->createElement('style', $css);
+        $styleAttribute = $document->createAttribute('type');
+        $styleAttribute->value = 'text/css';
+        $styleElement->appendChild($styleAttribute);
+
+        $bodyElement = $this->getBodyElement($document);
+        $bodyElement->appendChild($styleElement);
+    }
+
+    /**
+     * Checks that $document has a BODY element and adds it if it is missing.
+     *
+     * @param \DOMDocument $document
+     */
+    private function ensureExistenceOfBodyElement(\DOMDocument $document)
+    {
+        if ($document->getElementsByTagName('body')->item(0) !== null) {
+            return;
+        }
+
+        $htmlElement = $document->getElementsByTagName('html')->item(0);
+
+        $htmlElement->appendChild($document->createElement('body'));
+    }
+
+    /**
+     * Returns the BODY element.
+     *
+     * This method assumes that there always is a BODY element.
+     *
+     * @param \DOMDocument $document
+     *
+     * @return \DOMElement
+     *
+     * @throws \BadMethodCallException
+     */
+    private function getBodyElement(\DOMDocument $document)
+    {
+        $bodyElement = $document->getElementsByTagName('body')->item(0);
+        if ($bodyElement === null) {
+            throw new \BadMethodCallException(
+                'getBodyElement method may only be called after ensureExistenceOfBodyElement has been called.',
+                1508173775427
+            );
+        }
+
+        return $bodyElement;
+    }
+
+    /**
+     * Splits input CSS code to an array where:
+     *
+     * - key "css" will be contains clean CSS code
+     * - key "media" will be contains all valuable media queries
+     *
+     * Example:
+     *
+     * The CSS code
+     *
+     *   "@import "file.css"; h1 { color:red; } @media { h1 {}} @media tv { h1 {}}"
+     *
+     * will be parsed into the following array:
+     *
+     *   "css" => "h1 { color:red; }"
+     *   "media" => "@media { h1 {}}"
+     *
+     * @param string $css
+     *
+     * @return string[]
+     */
+    private function splitCssAndMediaQuery($css)
+    {
+        $cssWithoutComments = preg_replace('/\\/\\*.*\\*\\//sU', '', $css);
+
+        $mediaTypesExpression = '';
+        if (!empty($this->allowedMediaTypes)) {
+            $mediaTypesExpression = '|' . implode('|', array_keys($this->allowedMediaTypes));
+        }
+
+        $media = '';
+        $cssForAllowedMediaTypes = preg_replace_callback(
+            '#@media\\s+(?:only\\s)?(?:[\\s{\\(]\\s*' . $mediaTypesExpression . ')\\s*[^{]*+{.*}\\s*}\\s*#misU',
+            function ($matches) use (&$media) {
+                $media .= $matches[0];
+            },
+            $cssWithoutComments
+        );
+
+        // filter the CSS
+        $search = [
+            'import directives' => '/^\\s*@import\\s[^;]+;/misU',
+            'remaining media enclosures' => '/^\\s*@media\\s[^{]+{(.*)}\\s*}\\s/misU',
+        ];
+
+        $cleanedCss = preg_replace($search, '', $cssForAllowedMediaTypes);
+
+        return ['css' => $cleanedCss, 'media' => $media];
+    }
+
+    /**
+     * Creates a DOMDocument instance with the current HTML.
+     *
+     * @return \DOMDocument
+     */
+    private function createRawXmlDocument()
+    {
+        $xmlDocument = new \DOMDocument;
+        $xmlDocument->encoding = 'UTF-8';
+        $xmlDocument->strictErrorChecking = false;
+        $xmlDocument->formatOutput = true;
+        $libXmlState = libxml_use_internal_errors(true);
+        $xmlDocument->loadHTML($this->getUnifiedHtml());
+        libxml_clear_errors();
+        libxml_use_internal_errors($libXmlState);
+        $xmlDocument->normalizeDocument();
+
+        return $xmlDocument;
+    }
+
+    /**
+     * Returns the HTML with the unprocessable HTML tags removed and
+     * with added document type and Content-Type meta tag if needed.
+     *
+     * @return string the unified HTML
+     *
+     * @throws \BadMethodCallException
+     */
+    private function getUnifiedHtml()
+    {
+        $htmlWithoutUnprocessableTags = $this->removeUnprocessableTags($this->html);
+        $htmlWithDocumentType = $this->ensureDocumentType($htmlWithoutUnprocessableTags);
+
+        return $this->addContentTypeMetaTag($htmlWithDocumentType);
+    }
+
+    /**
+     * Removes the unprocessable tags from $html (if this feature is enabled).
+     *
+     * @param string $html
+     *
+     * @return string the reworked HTML with the unprocessable tags removed
+     */
+    private function removeUnprocessableTags($html)
+    {
+        if (empty($this->unprocessableHtmlTags)) {
+            return $html;
+        }
+
+        $unprocessableHtmlTags = implode('|', $this->unprocessableHtmlTags);
+
+        return preg_replace(
+            '/<\\/?(' . $unprocessableHtmlTags . ')[^>]*>/i',
+            '',
+            $html
+        );
+    }
+
+    /**
+     * Makes sure that the passed HTML has a document type.
+     *
+     * @param string $html
+     *
+     * @return string HTML with document type
+     */
+    private function ensureDocumentType($html)
+    {
+        $hasDocumentType = stripos($html, '<!DOCTYPE') !== false;
+        if ($hasDocumentType) {
+            return $html;
+        }
+
+        return self::DEFAULT_DOCUMENT_TYPE . $html;
+    }
+
+    /**
+     * Adds a Content-Type meta tag for the charset.
+     *
+     * @param string $html
+     *
+     * @return string the HTML with the meta tag added
+     */
+    private function addContentTypeMetaTag($html)
+    {
+        $hasContentTypeMetaTag = stripos($html, 'Content-Type') !== false;
+        if ($hasContentTypeMetaTag) {
+            return $html;
+        }
+
+        // We are trying to insert the meta tag to the right spot in the DOM.
+        // If we just prepended it to the HTML, we would lose attributes set to the HTML tag.
+        $hasHeadTag = stripos($html, '<head') !== false;
+        $hasHtmlTag = stripos($html, '<html') !== false;
+
+        if ($hasHeadTag) {
+            $reworkedHtml = preg_replace('/<head(.*?)>/i', '<head$1>' . self::CONTENT_TYPE_META_TAG, $html);
+        } elseif ($hasHtmlTag) {
+            $reworkedHtml = preg_replace(
+                '/<html(.*?)>/i',
+                '<html$1><head>' . self::CONTENT_TYPE_META_TAG . '</head>',
+                $html
+            );
+        } else {
+            $reworkedHtml = self::CONTENT_TYPE_META_TAG . $html;
+        }
+
+        return $reworkedHtml;
+    }
+
+    /**
+     * @param string[] $a
+     * @param string[] $b
+     *
+     * @return int
+     */
+    private function sortBySelectorPrecedence(array $a, array $b)
+    {
+        $precedenceA = $this->getCssSelectorPrecedence($a['selector']);
+        $precedenceB = $this->getCssSelectorPrecedence($b['selector']);
+
+        // We want these sorted in ascending order so selectors with lesser precedence get processed first and
+        // selectors with greater precedence get sorted last.
+        $precedenceForEquals = ($a['line'] < $b['line'] ? -1 : 1);
+        $precedenceForNotEquals = ($precedenceA < $precedenceB ? -1 : 1);
+        return ($precedenceA === $precedenceB) ? $precedenceForEquals : $precedenceForNotEquals;
+    }
+
+    /**
+     * @param string $selector
+     *
+     * @return int
+     */
+    private function getCssSelectorPrecedence($selector)
+    {
+        $selectorKey = md5($selector);
+        if (!isset($this->caches[self::CACHE_KEY_SELECTOR][$selectorKey])) {
+            $precedence = 0;
+            $value = 100;
+            // ids: worth 100, classes: worth 10, elements: worth 1
+            $search = ['\\#', '\\.', ''];
+
+            foreach ($search as $s) {
+                if (trim($selector) === '') {
+                    break;
+                }
+                $number = 0;
+                $selector = preg_replace('/' . $s . '\\w+/', '', $selector, -1, $number);
+                $precedence += ($value * $number);
+                $value /= 10;
+            }
+            $this->caches[self::CACHE_KEY_SELECTOR][$selectorKey] = $precedence;
+        }
+
+        return $this->caches[self::CACHE_KEY_SELECTOR][$selectorKey];
+    }
+
+    /**
+     * Maps a CSS selector to an XPath query string.
+     *
+     * @see http://plasmasturm.org/log/444/
+     *
+     * @param string $cssSelector a CSS selector
+     *
+     * @return string the corresponding XPath selector
+     */
+    private function translateCssToXpath($cssSelector)
+    {
+        $paddedSelector = ' ' . $cssSelector . ' ';
+        $lowercasePaddedSelector = preg_replace_callback(
+            '/\\s+\\w+\\s+/',
+            function (array $matches) {
+                return strtolower($matches[0]);
+            },
+            $paddedSelector
+        );
+        $trimmedLowercaseSelector = trim($lowercasePaddedSelector);
+        $xPathKey = md5($trimmedLowercaseSelector);
+        if (isset($this->caches[self::CACHE_KEY_XPATH][$xPathKey])) {
+            return $this->caches[self::CACHE_KEY_SELECTOR][$xPathKey];
+        }
+
+        $hasNotSelector = (bool)preg_match(
+            '/^([^:]+):not\\(\\s*([[:ascii:]]+)\\s*\\)$/',
+            $trimmedLowercaseSelector,
+            $matches
+        );
+        if (!$hasNotSelector) {
+            $xPath = '//' . $this->translateCssToXpathPass($trimmedLowercaseSelector);
+        } else {
+            /** @var string[] $matches */
+            $partBeforeNot = $matches[1];
+            $notContents = $matches[2];
+            $xPath = '//' . $this->translateCssToXpathPass($partBeforeNot) .
+                '[not(' . $this->translateCssToXpathPassInline($notContents) . ')]';
+        }
+        $this->caches[self::CACHE_KEY_SELECTOR][$xPathKey] = $xPath;
+
+        return $this->caches[self::CACHE_KEY_SELECTOR][$xPathKey];
+    }
+
+    /**
+     * Flexibly translates the CSS selector $trimmedLowercaseSelector to an xPath selector.
+     *
+     * @param string $trimmedLowercaseSelector
+     *
+     * @return string
+     */
+    private function translateCssToXpathPass($trimmedLowercaseSelector)
+    {
+        return $this->translateCssToXpathPassWithMatchClassAttributesCallback(
+            $trimmedLowercaseSelector,
+            [$this, 'matchClassAttributes']
+        );
+    }
+
+    /**
+     * Flexibly translates the CSS selector $trimmedLowercaseSelector to an xPath selector for inline usage.
+     *
+     * @param string $trimmedLowercaseSelector
+     *
+     * @return string
+     */
+    private function translateCssToXpathPassInline($trimmedLowercaseSelector)
+    {
+        return $this->translateCssToXpathPassWithMatchClassAttributesCallback(
+            $trimmedLowercaseSelector,
+            [$this, 'matchClassAttributesInline']
+        );
+    }
+
+    /**
+     * Flexibly translates the CSS selector $trimmedLowercaseSelector to an xPath selector while using
+     * $matchClassAttributesCallback as to match the class attributes.
+     *
+     * @param string $trimmedLowercaseSelector
+     * @param callable $matchClassAttributesCallback
+     *
+     * @return string
+     */
+    private function translateCssToXpathPassWithMatchClassAttributesCallback(
+        $trimmedLowercaseSelector,
+        callable $matchClassAttributesCallback
+    ) {
+        $roughXpath = preg_replace(array_keys($this->xPathRules), $this->xPathRules, $trimmedLowercaseSelector);
+        $xPathWithIdAttributeMatchers = preg_replace_callback(
+            self::ID_ATTRIBUTE_MATCHER,
+            [$this, 'matchIdAttributes'],
+            $roughXpath
+        );
+        $xPathWithIdAttributeAndClassMatchers = preg_replace_callback(
+            self::CLASS_ATTRIBUTE_MATCHER,
+            $matchClassAttributesCallback,
+            $xPathWithIdAttributeMatchers
+        );
+
+        // Advanced selectors are going to require a bit more advanced emogrification.
+        $xPathWithIdAttributeAndClassMatchers = preg_replace_callback(
+            '/([^\\/]+):nth-child\\(\\s*(odd|even|[+\\-]?\\d|[+\\-]?\\d?n(\\s*[+\\-]\\s*\\d)?)\\s*\\)/i',
+            [$this, 'translateNthChild'],
+            $xPathWithIdAttributeAndClassMatchers
+        );
+        $finalXpath = preg_replace_callback(
+            '/([^\\/]+):nth-of-type\\(\s*(odd|even|[+\\-]?\\d|[+\\-]?\\d?n(\\s*[+\\-]\\s*\\d)?)\\s*\\)/i',
+            [$this, 'translateNthOfType'],
+            $xPathWithIdAttributeAndClassMatchers
+        );
+
+        return $finalXpath;
+    }
+
+    /**
+     * @param string[] $match
+     *
+     * @return string
+     */
+    private function matchIdAttributes(array $match)
+    {
+        return ($match[1] !== '' ? $match[1] : '*') . '[@id="' . $match[2] . '"]';
+    }
+
+    /**
+     * @param string[] $match
+     *
+     * @return string xPath class attribute query wrapped in element selector
+     */
+    private function matchClassAttributes(array $match)
+    {
+        return ($match[1] !== '' ? $match[1] : '*') . '[' . $this->matchClassAttributesInline($match) . ']';
+    }
+
+    /**
+     * @param string[] $match
+     *
+     * @return string xPath class attribute query
+     */
+    private function matchClassAttributesInline(array $match)
+    {
+        return 'contains(concat(" ",@class," "),concat(" ","' .
+            implode(
+                '"," "))][contains(concat(" ",@class," "),concat(" ","',
+                explode('.', substr($match[2], 1))
+            ) . '"," "))';
+    }
+
+    /**
+     * @param string[] $match
+     *
+     * @return string
+     */
+    private function translateNthChild(array $match)
+    {
+        $parseResult = $this->parseNth($match);
+
+        if (isset($parseResult[self::MULTIPLIER])) {
+            if ($parseResult[self::MULTIPLIER] < 0) {
+                $parseResult[self::MULTIPLIER] = abs($parseResult[self::MULTIPLIER]);
+                $xPathExpression = sprintf(
+                    '*[(last() - position()) mod %1%u = %2$u]/self::%3$s',
+                    $parseResult[self::MULTIPLIER],
+                    $parseResult[self::INDEX],
+                    $match[1]
+                );
+            } else {
+                $xPathExpression = sprintf(
+                    '*[position() mod %1$u = %2$u]/self::%3$s',
+                    $parseResult[self::MULTIPLIER],
+                    $parseResult[self::INDEX],
+                    $match[1]
+                );
+            }
+        } else {
+            $xPathExpression = sprintf('*[%1$u]/self::%2$s', $parseResult[self::INDEX], $match[1]);
+        }
+
+        return $xPathExpression;
+    }
+
+    /**
+     * @param string[] $match
+     *
+     * @return string
+     */
+    private function translateNthOfType(array $match)
+    {
+        $parseResult = $this->parseNth($match);
+
+        if (isset($parseResult[self::MULTIPLIER])) {
+            if ($parseResult[self::MULTIPLIER] < 0) {
+                $parseResult[self::MULTIPLIER] = abs($parseResult[self::MULTIPLIER]);
+                $xPathExpression = sprintf(
+                    '%1$s[(last() - position()) mod %2$u = %3$u]',
+                    $match[1],
+                    $parseResult[self::MULTIPLIER],
+                    $parseResult[self::INDEX]
+                );
+            } else {
+                $xPathExpression = sprintf(
+                    '%1$s[position() mod %2$u = %3$u]',
+                    $match[1],
+                    $parseResult[self::MULTIPLIER],
+                    $parseResult[self::INDEX]
+                );
+            }
+        } else {
+            $xPathExpression = sprintf('%1$s[%2$u]', $match[1], $parseResult[self::INDEX]);
+        }
+
+        return $xPathExpression;
+    }
+
+    /**
+     * @param string[] $match
+     *
+     * @return int[]
+     */
+    private function parseNth(array $match)
+    {
+        if (in_array(strtolower($match[2]), ['even', 'odd'], true)) {
+            // we have "even" or "odd"
+            $index = strtolower($match[2]) === 'even' ? 0 : 1;
+            return [self::MULTIPLIER => 2, self::INDEX => $index];
+        }
+        if (stripos($match[2], 'n') === false) {
+            // if there is a multiplier
+            $index = (int)str_replace(' ', '', $match[2]);
+            return [self::INDEX => $index];
+        }
+
+        if (isset($match[3])) {
+            $multipleTerm = str_replace($match[3], '', $match[2]);
+            $index = (int)str_replace(' ', '', $match[3]);
+        } else {
+            $multipleTerm = $match[2];
+            $index = 0;
+        }
+
+        $multiplier = str_ireplace('n', '', $multipleTerm);
+
+        if ($multiplier === '') {
+            $multiplier = 1;
+        } elseif ($multiplier === '0') {
+            return [self::INDEX => $index];
+        } else {
+            $multiplier = (int)$multiplier;
+        }
+
+        while ($index < 0) {
+            $index += abs($multiplier);
+        }
+
+        return [self::MULTIPLIER => $multiplier, self::INDEX => $index];
+    }
+
+    /**
+     * Parses a CSS declaration block into property name/value pairs.
+     *
+     * Example:
+     *
+     * The declaration block
+     *
+     *   "color: #000; font-weight: bold;"
+     *
+     * will be parsed into the following array:
+     *
+     *   "color" => "#000"
+     *   "font-weight" => "bold"
+     *
+     * @param string $cssDeclarationsBlock the CSS declarations block without the curly braces, may be empty
+     *
+     * @return string[]
+     *         the CSS declarations with the property names as array keys and the property values as array values
+     */
+    private function parseCssDeclarationsBlock($cssDeclarationsBlock)
+    {
+        if (isset($this->caches[self::CACHE_KEY_CSS_DECLARATIONS_BLOCK][$cssDeclarationsBlock])) {
+            return $this->caches[self::CACHE_KEY_CSS_DECLARATIONS_BLOCK][$cssDeclarationsBlock];
+        }
+
+        $properties = [];
+        $declarations = preg_split('/;(?!base64|charset)/', $cssDeclarationsBlock);
+
+        foreach ($declarations as $declaration) {
+            $matches = [];
+            if (!preg_match('/^([A-Za-z\\-]+)\\s*:\\s*(.+)$/', trim($declaration), $matches)) {
+                continue;
+            }
+
+            $propertyName = strtolower($matches[1]);
+            $propertyValue = $matches[2];
+            $properties[$propertyName] = $propertyValue;
+        }
+        $this->caches[self::CACHE_KEY_CSS_DECLARATIONS_BLOCK][$cssDeclarationsBlock] = $properties;
+
+        return $properties;
+    }
+
+    /**
+     * Find the nodes that are not to be emogrified.
+     *
+     * @param \DOMXPath $xPath
+     *
+     * @return \DOMElement[]
+     *
+     * @throws \InvalidArgumentException
+     */
+    private function getNodesToExclude(\DOMXPath $xPath)
+    {
+        $excludedNodes = [];
+        foreach (array_keys($this->excludedSelectors) as $selectorToExclude) {
+            try {
+                $matchingNodes = $xPath->query($this->translateCssToXpath($selectorToExclude));
+            } catch (\InvalidArgumentException $e) {
+                if ($this->debug) {
+                    throw $e;
+                }
+                continue;
+            }
+            foreach ($matchingNodes as $node) {
+                $excludedNodes[] = $node;
+            }
+        }
+
+        return $excludedNodes;
+    }
+
+    /**
+     * Handles invalid xPath expression warnings, generated during the process() method,
+     * during querying \DOMDocument and trigger \InvalidArgumentException with invalid selector
+     * or \RuntimeException, depending on the source of the warning.
+     *
+     * @param int $type
+     * @param string $message
+     * @param string $file
+     * @param int $line
+     * @param array $context
+     *
+     * @return bool always false
+     *
+     * @throws \InvalidArgumentException
+     * @throws \RuntimeException
+     */
+    public function handleXpathQueryWarnings( // @codingStandardsIgnoreLine
+        $type,
+        $message,
+        $file,
+        $line,
+        array $context
+    ) {
+        $selector = '';
+        if (isset($context['cssRule']['selector'])) {
+            // warnings generated by invalid/unrecognized selectors in method process()
+            $selector = $context['cssRule']['selector'];
+        } elseif (isset($context['selectorToExclude'])) {
+            // warnings generated by invalid/unrecognized selectors in method getNodesToExclude()
+            $selector = $context['selectorToExclude'];
+        } elseif (isset($context['cssSelector'])) {
+            // warnings generated by invalid/unrecognized selectors in method existsMatchForCssSelector()
+            $selector = $context['cssSelector'];
+        }
+
+        if ($selector !== '') {
+            throw new \InvalidArgumentException(
+                sprintf('%1$s in selector >> %2$s << in %3$s on line %4$u', $message, $selector, $file, $line),
+                1509279985
+            );
+        }
+
+        // Catches eventual warnings generated by method getAllNodesWithStyleAttribute()
+        if (isset($context['xPath'])) {
+            throw new \RuntimeException(
+                sprintf('%1$s in %2$s on line %3$u', $message, $file, $line),
+                1509280067
+            );
+        }
+
+        // the normal error handling continues when handler return false
+        return false;
+    }
+
+    /**
+     * Sets the debug mode.
+     *
+     * @param bool $debug set to true to enable debug mode
+     *
+     * @return void
+     */
+    public function setDebug($debug)
+    {
+        $this->debug = $debug;
+    }
 }
diff --git a/includes/wc-update-functions.php b/includes/wc-update-functions.php
index ba56e596ab2..c564831bbdf 100644
--- a/includes/wc-update-functions.php
+++ b/includes/wc-update-functions.php
@@ -1835,3 +1835,130 @@ function wc_update_343_cleanup_foreign_keys() {
 function wc_update_343_db_version() {
 	WC_Install::update_db_version( '3.4.3' );
 }
+
+/**
+ * Copy order customer_id from post meta to post_author and set post_author to 0 for refunds.
+ *
+ * Two different strategies are used to copy data depending if the update is being executed from
+ * the command line or not. If `wp wc update` is used to update the database, this function
+ * copies data in a single go that is faster but uses more resources. If the databse update was
+ * triggered from the wp-admin, this function copies data in batches which is slower but uses
+ * few resources and thus is less likely to fail on smaller servers.
+ *
+ * @param WC_Background_Updater|false $updater Background updater instance or false if function is called from `wp wc update` WP-CLI command.
+ * @return true|void Return true if near memory limit and needs to restart. Return void if update completed.
+ */
+function wc_update_350_order_customer_id( $updater = false ) {
+	global $wpdb;
+
+	$post_types              = (array) apply_filters( 'woocommerce_update_350_order_customer_id_post_types', array( 'shop_order' ) );
+	$post_types_placeholders = implode( ', ', array_fill( 0, count( $post_types ), '%s' ) );
+
+	if ( defined( 'WP_CLI' ) && WP_CLI ) {
+		// If running the update from the command-line, copy data in a single go which is faster but uses more resources.
+		$wpdb->query(
+			'CREATE TEMPORARY TABLE customers_map (post_id BIGINT(20), customer_id BIGINT(20), PRIMARY KEY(post_id))'
+		);
+
+		$wpdb->query(
+			"INSERT IGNORE INTO customers_map (SELECT post_id, meta_value FROM wp_postmeta WHERE meta_key = '_customer_user')"
+		);
+
+		$wpdb->query( 'SET sql_safe_updates=1' );
+
+		$wpdb->query(
+			$wpdb->prepare(
+				"UPDATE wp_posts JOIN customers_map ON wp_posts.ID = customers_map.post_id SET wp_posts.post_author = customers_map.customer_id WHERE post_type IN ({$post_types_placeholders})",  // phpcs:ignore WordPress.WP.PreparedSQL.NotPrepared
+				$post_types
+			)
+		);
+
+		$wpdb->update( $wpdb->posts, array( 'post_author' => 0 ), array( 'post_type' => 'shop_order_refund' ) );
+	} else {
+		// If running the update from the wp-admin, copy data in batches being careful not to use more memory than allowed.
+		$admin_orders_sql = '';
+		$admin_orders     = get_transient( 'wc_update_350_admin_orders' );
+
+		if ( false === $admin_orders ) {
+			// Get the list of orders that we don't want to change as they belong to user ID 1.
+			$admin_orders = $wpdb->get_col(
+				$wpdb->prepare(
+					"SELECT ID FROM wp_posts p
+					INNER JOIN wp_postmeta pm ON p.ID = pm.post_id
+					WHERE post_type IN ({$post_types_placeholders}) AND meta_key = '_customer_user' AND meta_value = 1", // phpcs:ignore WordPress.WP.PreparedSQL.NotPrepared
+					$post_types
+				)
+			);
+
+			// Cache the list of orders placed by the user ID 1 as to large stores this query can be slow.
+			set_transient( 'wc_update_350_admin_orders', $admin_orders, DAY_IN_SECONDS );
+		}
+
+		if ( ! empty( $admin_orders ) ) {
+			$admin_orders_sql .= ' AND ID NOT IN (' . implode( ', ', $admin_orders ) . ') ';
+		}
+
+		// Query to get a batch of orders IDs to change.
+		$query = $wpdb->prepare(
+			// phpcs:disable WordPress.WP.PreparedSQL.NotPrepared
+			"SELECT ID FROM {$wpdb->posts}
+			WHERE post_author = 1 AND post_type IN ({$post_types_placeholders}) $admin_orders_sql
+			LIMIT 1000",
+			$post_types
+			// phpcs:enable
+		);
+
+		while ( true ) {
+			// phpcs:ignore WordPress.WP.PreparedSQL.NotPrepared
+			$orders_to_update = $wpdb->get_col( $query );
+
+			// Exit loop if no more orders to update.
+			if ( ! $orders_to_update ) {
+				break;
+			}
+
+			$orders_meta_data = $wpdb->get_results(
+				// phpcs:ignore WordPress.WP.PreparedSQL.NotPrepared
+				"SELECT post_id, meta_value as customer_id FROM {$wpdb->postmeta} WHERE meta_key = '_customer_user' AND post_id IN (" . implode( ', ', $orders_to_update ) . ')'
+			);
+
+			// Exit loop if no _customer_user metas exist for the list of orders to update.
+			if ( ! $orders_meta_data ) {
+				break;
+			}
+
+			// Update post_author for a batch of orders.
+			foreach ( $orders_meta_data as $order_meta ) {
+				// Stop update execution and re-enqueue it if near memory limit.
+				if ( $updater instanceof WC_Background_Updater && $updater->is_memory_exceeded() ) {
+					return true;
+				}
+
+				$wpdb->update( $wpdb->posts, array( 'post_author' => $order_meta->customer_id ), array( 'ID' => $order_meta->post_id ) );
+			}
+		}
+
+		// Set post_author to 0 instead of 1 on all shop_order_refunds.
+		while ( true ) {
+			// Stop update execution and re-enqueue it if near memory limit.
+			if ( $updater instanceof WC_Background_Updater && $updater->is_memory_exceeded() ) {
+				return true;
+			}
+
+			$updated_rows = $wpdb->query( "UPDATE {$wpdb->posts} SET post_author = 0 WHERE post_type = 'shop_order_refund' LIMIT 1000" );
+
+			if ( ! $updated_rows ) {
+				break;
+			}
+		}
+	}
+
+	wp_cache_flush();
+}
+
+/**
+ * Update DB Version.
+ */
+function wc_update_350_db_version() {
+	WC_Install::update_db_version( '3.5.0' );
+}
diff --git a/includes/wc-user-functions.php b/includes/wc-user-functions.php
index a302ce008bf..b8f62fa7bc8 100644
--- a/includes/wc-user-functions.php
+++ b/includes/wc-user-functions.php
@@ -219,11 +219,15 @@ function wc_customer_bought_product( $customer_email, $user_id, $product_id ) {
 	$result         = get_transient( $transient_name );
 
 	if ( false === $result ) {
-		$customer_data = array( $user_id );
+		$customer_data = array();
 
 		if ( $user_id ) {
 			$user = get_user_by( 'id', $user_id );
 
+			if ( version_compare( get_option( 'woocommerce_db_version' ), '3.5.0', '<' ) ) {
+				$customer_data[] = $user_id;
+			}
+
 			if ( isset( $user->user_email ) ) {
 				$customer_data[] = $user->user_email;
 			}
@@ -240,19 +244,31 @@ function wc_customer_bought_product( $customer_email, $user_id, $product_id ) {
 			return false;
 		}
 
-		$result = $wpdb->get_col(
-			"
-			SELECT im.meta_value FROM {$wpdb->posts} AS p
-			INNER JOIN {$wpdb->postmeta} AS pm ON p.ID = pm.post_id
-			INNER JOIN {$wpdb->prefix}woocommerce_order_items AS i ON p.ID = i.order_id
-			INNER JOIN {$wpdb->prefix}woocommerce_order_itemmeta AS im ON i.order_item_id = im.order_item_id
-			WHERE p.post_status IN ( 'wc-" . implode( "','wc-", $statuses ) . "' )
-			AND pm.meta_key IN ( '_billing_email', '_customer_user' )
-			AND im.meta_key IN ( '_product_id', '_variation_id' )
-			AND im.meta_value != 0
-			AND pm.meta_value IN ( '" . implode( "','", $customer_data ) . "' )
-		"
-		); // WPCS: unprepared SQL ok.
+		if ( version_compare( get_option( 'woocommerce_db_version' ), '3.5.0', '>=' ) && $user_id ) {
+			// Since WC 3.5 wp_posts.post_author is used to store the ID of the customer who placed an order.
+			$query = "SELECT im.meta_value FROM {$wpdb->posts} AS p
+				INNER JOIN {$wpdb->postmeta} AS pm ON p.ID = pm.post_id
+				INNER JOIN {$wpdb->prefix}woocommerce_order_items AS i ON p.ID = i.order_id
+				INNER JOIN {$wpdb->prefix}woocommerce_order_itemmeta AS im ON i.order_item_id = im.order_item_id
+				WHERE p.post_status IN ( 'wc-" . implode( "','wc-", $statuses ) . "' )
+				AND p.post_author = {$user_id}
+				AND pm.meta_key = '_billing_email'
+				AND im.meta_key IN ( '_product_id', '_variation_id' )
+				AND im.meta_value != 0
+				AND pm.meta_value IN ( '" . implode( "','", $customer_data ) . "' )";
+		} else {
+			$query = "SELECT im.meta_value FROM {$wpdb->posts} AS p
+				INNER JOIN {$wpdb->postmeta} AS pm ON p.ID = pm.post_id
+				INNER JOIN {$wpdb->prefix}woocommerce_order_items AS i ON p.ID = i.order_id
+				INNER JOIN {$wpdb->prefix}woocommerce_order_itemmeta AS im ON i.order_item_id = im.order_item_id
+				WHERE p.post_status IN ( 'wc-" . implode( "','wc-", $statuses ) . "' )
+				AND pm.meta_key IN ( '_billing_email', '_customer_user' )
+				AND im.meta_key IN ( '_product_id', '_variation_id' )
+				AND im.meta_value != 0
+				AND pm.meta_value IN ( '" . implode( "','", $customer_data ) . "' )";
+		}
+
+		$result = $wpdb->get_col( $query ); // WPCS: unprepared SQL ok.
 		$result = array_map( 'absint', $result );
 
 		set_transient( $transient_name, $result, DAY_IN_SECONDS * 30 );
@@ -495,7 +511,7 @@ function wc_get_customer_order_count( $user_id ) {
 }
 
 /**
- * Reset _customer_user on orders when a user is deleted.
+ * Reset customer ID on orders when a user is deleted.
  *
  * @param int $user_id User ID.
  */
@@ -508,6 +524,22 @@ function wc_reset_order_customer_id_on_deleted_user( $user_id ) {
 			'meta_value' => $user_id,
 		)
 	); // WPCS: slow query ok.
+
+	$post_types              = (array) apply_filters( 'woocommerce_reset_order_customer_id_post_types', array( 'shop_order' ) );
+	$post_types_placeholders = implode( ', ', array_fill( 0, count( $post_types ), '%s' ) );
+	$query_args              = array_merge( $post_types, array( $user_id ) );
+
+	// Since WC 3.5, the customer ID is stored both in the _customer_user postmeta and in the post_author field.
+	// In future versions of WC, the plan is to use only post_author and stop using _customer_user, but for now
+	// we have to update both places.
+	$wpdb->query(
+		// phpcs:disable WordPress.WP.PreparedSQL.NotPrepared, WordPress.DB.PreparedSQLPlaceholders.UnfinishedPrepare
+		$wpdb->prepare(
+			"UPDATE {$wpdb->posts} SET `post_author` = 0 WHERE post_type IN ({$post_types_placeholders}) AND post_author = %d",
+			$query_args
+		)
+		// phpcs:enable
+	);
 }
 
 add_action( 'deleted_user', 'wc_reset_order_customer_id_on_deleted_user' );