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+<!-- START doctoc generated TOC please keep comment here to allow auto update -->
+<!-- DON'T EDIT THIS SECTION, INSTEAD RE-RUN doctoc TO UPDATE -->
+## Table of Contents
+
+- [Prefixing](#prefixing)
+- [Class names](#class-names)
+  - [Example](#example)
+
+<!-- END doctoc generated TOC please keep comment here to allow auto update -->
+
+# PHP
+
+WooCommerce core follows [WordPress PHP naming conventions](https://make.wordpress.org/core/handbook/best-practices/coding-standards/php/#naming-conventions). On top of that, function, class, and hook names should be prefixed. For functions the prefix is `wc_`, for classes is `WC_` and for hooks is `woocommerce_`.
+
+Function name examples:
+
+- `wc_get_product()`
+- `wc_is_active_theme()`
+
+Class name examples:
+
+- `WC_Breadcrumb`
+- `WC_Cart`
+
+Hook name examples (actions or filters):
+
+- `woocommerce_after_checkout_validation`
+- `woocommerce_get_formatted_order_total`
+
+# JS
+
+Use [WordPress JS naming conventions](https://developer.wordpress.org/coding-standards/wordpress-coding-standards/javascript/#naming-conventions).
+
+# CSS and SASS
+
+Our guidelines are based on those used in [Calypso](https://github.com/Automattic/wp-calypso), which itself follows the BEM methodology. Refer to [this doc](https://wpcalypso.wordpress.com/devdocs/docs/coding-guidelines/css.md?term=css) for full details. There are a few differences in WooCommerce however which are outlined below;
+
+### Prefixing
+As a WordPress plugin WooCommerce has to play nicely with WordPress core and other plugins/themes. To minimize conflict potential, all classes should be prefixed with `.woocommerce-`.
+
+### Class names
+Calypso is built in React and uses component names to formulate CSS class names. WooCommerce Core has none of these components, so it uses a more traditional [BEM](http://getbem.com/) approach to [naming classes](http://cssguidelin.es/#bem-like-naming). 
+
+When adding classes remember:
+
+* **Block** - Standalone entity that is meaningful on its own.
+* **Element** - Parts of a block and have no standalone meaning. They are semantically tied to their block.
+* **Modifier** - Flags on blocks or elements. Use them to change appearance or behavior.
+
+#### Example
+* `.woocommerce-loop {}` (block).
+* `.woocommerce-loop-product {}` (nested block).
+* `.woocommerce-loop-product--sale {}` (modifier).
+* `.woocommerce-loop-product__link {}` (element).
+* `.woocommerce-loop-product__title {}` (element).
+* `.woocommerce-loop-product__price {}` (element).
+* `.woocommerce-loop-product__rating {}` (element).
+* `.woocommerce-loop-product__button-add-to-cart {}` (element).
+* `.woocommerce-loop-product__button-add-to-cart--added {}` (modifier).
+
+**Note:** `.woocommerce-loop-product` is not the chosen class name _because_ the block is nested within `.woocommerce-loop`. It's to be specific so that we can have separate classes for single products, cart products, etc. _Nested blocks do not need to inherit their parent's full name_.
+
+You can read more about BEM key concepts [here](https://en.bem.info/methodology/key-concepts/).
+
+**TL;DR**
+
+- Follow the [WP Coding standards for CSS](https://make.wordpress.org/core/handbook/best-practices/coding-standards/css/) unless it contradicts anything here.
+- Follow [Calypso guidelines](https://wpcalypso.wordpress.com/devdocs/docs/coding-guidelines/css.md?term=css).
+- Use BEM for [class names](https://en.bem.info/methodology/naming-convention/).
+- Prefix all the things.
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