http://en.wikipedia.org/wiki/Wikipedia:Category

This highly-readable article explains (to both users and contributors) how to use and work with categories. It is packed with common sense ideas and explicit MediaWiki how-to's.

Thanks for your suggestion.

Whilst the Wikipedia categorization article contains some useful information, much of it is specific to Wikipedia. Since every page in Moodle has a link to a corresponding page in Moodle Docs, categorization is not as important as for Wikipedia. However, it would be helpful if further explanation of categorization could be added to http://docs.moodle.org/en/MoodleDocs:Style_guide.