TIL, that's amazing! :D

EDIT: Turns out, I spoke too soon, there is no such option according to docs or from reading the code, maybe you have another plugin doing this?

EDIT2: found it: https://github.com/keith/edit-weechat

Whoops, sorry about that. I'll have to double check I was 90% that was standard in weechat or wee-slack - I've installed very few non-standard plug-ins.