However, before coming up with a zillion suggestions about how to make the syntax nicer, please do consider the idea that we did put a lot of thought into the diff syntax, and that covering all the uses and edge cases and is not easy.
Right. And I don't think most people disagree with that. However, I also think that some sort of shorthand mechanism would greatly help the "verbosity problem". We have a situation where the simplest things are very short and very complex things are very long (both of which are quite reasonable), but there doesn't seem to be much in the middle and I think the issue is how to add that. I think RTH's suggestion of using a "+" or similar symbol to indicate the root is a good one. Another possibility (not mutually exclusive with that one) is to have some shorthand like using ".." in a context where a URL is required to "do the right thing". (Obviously an issue here is in determining whether something is a URL or filename, so maybe something like "%.." or "-.." is needed.)