Referencing footnotes with numbers in brackets is a very common convention in email and plaintext or close-to-plaintext formats:
the multimedia team [1] had a chat about some architectural issues with MultimediaViewer [2] today, and Robla has pointed out that we should publish such discussions on wikitech-l to make sure we do no reinvent to many wheels, so here goes. Comments pointing out all the obvious solutions we have missed are very welcome. [1] https://www.mediawiki.org/wiki/Multimedia [2] https://www.mediawiki.org/wiki/Extension:MultimediaViewer
The reference list doesn't look so great in Remarkup:
[1] https://www.mediawiki.org/wiki/Multimedia
[2] https://www.mediawiki.org/wiki/Extension:MultimediaViewer
Using [X]/[x] is a nice, intuitive syntax for checkboxes, but there is no reason to pick up anything within brackets - if it's not X, it should just be left as it is.