I was wondering what The metadata values can contain absolutely anything you like -- but you're recommended to keep it simple and reasonably short. listed on the metadata page really means?

Here is my use case (which is part of a larger solution)...

I've been storing my photos in git annex for a while (years perhaps), I (or actually the wife) tried to find one and couldn't, so I'm thinking I need to add metadata (Tags and captions, etc) to each picture. I was looking for ways to do so. I was actually considering using gthumb or shotwell or similar to create the tags and somehow pull that out and associate it with the file (either with a plugin or program) and then sort out how to distribute the metadata with the pics. The git annex metadata seems like a reasonable solution for keeping metadata with the pictures. The question is in this case, how long can the text in say a caption tag before git-annex has problems? I could probably do something like caption- to handle really long captions, but then captions are short by definition, so perhaps I should say description instead. And for this particular use case, I am aware this doesn't solve the problem of actually creating the data, just trying to sort out if get annex metadata to the right solution to tie the metadata to a pic, err file.