I've asked a few questions at https://phabricator.wikimedia.org/T95076 that someone here might be able to help with, namely:

1. What accessibility issues need to be considered, for using tooltips in form fields? (e.g. old browsers, screen-readers, accesskeys) 2. Do we have any mediawiki guidelines on what developers/extensions should use? (and should they be linked in the Living-Style-Guide https://phabricator.wikimedia.org/tag/living-style-guide/ e.g. here http://livingstyleguide.wmflabs.org/wiki/Inputs or is that outside of it's remit?) 3. What is the best external documentation, and "best in class" examples? 4. Where do we currently store some examples? e.g. the title="Enter a short summary [Alt+Shift+b]" in enwiki's edit-summary field. 5. What pragmatic limits are there, on the formatting & length of tooltip content? (can we do split lines in basic HTML? How much harder is it to get clickable links in them? F108798 https://phabricator.wikimedia.org/F108798: this is very pretty, but the rendered HTML is gigantic, and it's still not clickable/copyable text.) 6. What other things should I/we be asking?

Answers over there, please and thank you. :)