FYI something else that might be worth looking into (which I happened to implement for iXForms) is allow clickable URL links in question hints. eg
<label>Hint with link</label>
<hint>For more information see <a href="http://en.wikipedia.org/wiki/XForms">Wikipedia</a></hint>
Basically it allows you to hook in extensive additional question-specific background information/documentation via the hint, eg you could have a hint with "Tree Height Measurement" link to your image at https://getodk-a3b1.kxcdn.com/uploads/default/original/2X/a/aa9e2463cd03684f6d956c3c7393130eeba078bc.png
Although I'm linking to an actual web page above, with a bit of cleverness (and appropriate URL) you could easily have the link refer to an on-device media file, eg image, movie, HTML document, PDF, etc that is associated with the form.
Moved this from a Support thread since its basically proposing a new feature - one I've implemented in iXForms, and which I think might be a useful addition to Collect.
FYI there is an existing URL widget that accomplishes a similar result, albeit outside of a hint. So adding this feature probably isnt so compelling... Thnx @yanokwa !
Also, we had inline HTML for labels and hints at some point, but are moving away from that in favor of Markdown. https://docs.opendatakit.org/form-styling/#inline-html describes why.
Thnx for link. It seemed like a good idea at the time, but I'm inclined to deprecate mine (too). Its a real nuisance to handle embedded URLs in the XForm to prevent them throwing my SAX parser off when processing form definitions. Far easier to have markdown in the label/hint strings and parse them appropriately when displaying the form much later.
Closing this topic/withdrawing feature request because desired functionality is covered better elsewhere.