just-the-docs/docs/tests/navigation/order/default/index.md

layout	title	parent	nav_order	has_children
default	Default	Tests for order	1	true

Default Order

When nav_order fields are omitted, the pages are ordered alphabetically by their titles.

By default, all Capital letters come before all lowercase letters; you can add nav_sort: case_insensitive in the configuration file to ignore the case).

Digits precede letters, and numeric titles are ordered lexicographically: 10 precedes 2 (in contrast to explicit numeric nav_order values).