Collation is the process of ordering a list of items. For example, you might collate a list of 15, 8, and 7 with a numerical collation in ascending order, so that your collated list would be 7, 8, and 15.
MediaWiki provides several options for collation:
- Unicode Collation Algorithm (UCA), either language-agnostic (uca-default) or language-specific (uca-xx). This algorithm typically groups letters with diacritics with the non-diacritic version.
- Uppercase, a simple algorithm that sorts based on character value, but considers uppercase and lowercase letters the same
- Identity, same as uppercase but doesn't group uppercase and lowercase together.
As of May 2016, the default category collation for Wikimedia wikis is "uppercase", while several dozen wikis override this default.
For the non-default settings, see the values per wiki in the section
wgCategoryCollation in the file https://noc.wikimedia.org/conf/InitialiseSettings.php.txt