+1. (There's a similar thread at https://www.mediawiki.org/wiki/Topic:Tm0pld07rfuoifsy where the editor is asking for the ability to add "incategory:foo", without having to resort to the "default=" parameter - which can confuse the end-users, and means they have to both avoid deleting it, and add a space afterwards before they can begin typing.)

Hmm, and I think this might be a duplicate of the older T32404: InputBox:Possibility to insert entered string in a predefined search containing boolean operators.

I am interested in implementing something like this, but instead of hardcoding every possible CirrusSearch filter into the extension, allow freeform text to append to the search term where the filters could be defined. Such that you'd have searchfilters=incategory:Blah inlanguage: ja etc. This is both easier to implement and would mean we would not have to change the extension whenever CirrusSearch is also changed. Would this approach work for people?

Upon conferring with @Quiddity I think the best option is to not merge this task with T32404 as that task asks for something a lot more sophisticated than this task.

Change 357437 had a related patch set uploaded (by Harej; owner: Harej):
[mediawiki/extensions/InputBox@master] Allow appending searchfilters to terms

https://gerrit.wikimedia.org/r/357437

Change 357437 merged by jenkins-bot:
[mediawiki/extensions/InputBox@master] Allow appending searchfilters to terms

https://gerrit.wikimedia.org/r/357437

I've added docs at https://www.mediawiki.org/w/index.php?title=Extension:InputBox&diff=2493340&oldid=2467274 (please always remember to add docs, for new features! Thanks!)