Add categories to en:wikisource the normal way (as category tags)

[wrought]

The "category" element of the Template:Header on wikisource is not very important, nor necessarily standard.

Because of #12 we should work around this. Instead, we should simply add normal category wikilinks, e.g. [[Category:Evolutionary biology]]

[wrought]

note, however, that this was done too: https://en.wikisource.org/wiki/Template_talk:Header#Change_to_Support_More_than_10_Categories