I've been using Textastic + Working Copy as my personal notes app on iOS for a couple of months, on my desktop pc I edit my files in neovim and use vimwiki. Syntax support is close to MediaWiki, but any additional syntax support would be awesome as well.
My main suggestion: I was wondering if following links could be added. Feature might need some tweaking to not introduce unexpected behaviour, so maybe a second tap to confirm a link follow. This feature could also be extended to html, including opening associated css and other linked content, and while I think about it, source code includes and imports like include "code.h" and import banana, or from banana import skin. Some links might need hints to follow links, for example MediaWiki links would not include the .wiki extension; Python could be interesting in searching for banana.py and banana/__init__.py.
I would think in most cases only the text that applies to the linking would be active, like code.h and banana in the above examples. UI clues could just be an underline of some type. When a link can't be followed, I would think the software simply doing nothing (other than potentially adjusting the cursor location) and not notifying the user is better.
Linking it external content, like triggering a web browser is in the realm of nice to have; and also recognising a URI and triggering from there could also be useful.
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