[jlgtx]

However, MS can't be responsible for correcting for mistakes in pro files,
after all, some songs don't necessarily start or end in the same chord as the key directive.
I prefer it this way, just make sure the pro files are correct.

And therein lies the key (ha!). The ChordPro format reminds me very much of the early days of HTML, when you could hand-code pretty much whatever you wanted, but if you didn't pay close attention to the standard, your page might look very different in different browsers. At first glance, ChordPro seems somewhat "loosey-goosey" in terms of what you can do with the formatting; e.g. "Well, the song is actually in E, but I've already transposed the chords into D so I'll embed those in the lyrics, but I'll put {key: E} at the top to remind me of the original key, and oh yeah I should add {capo:2} to remind myself to use a capo," makes sense from a certain standpoint but is incorrect according to the standard.

In my own usage, I have long been embedding "pipe" symbols [|] to denote measure downbeats, and some ChordPro display apps have not liked that at all. I just now looked it up, and it turns out the standard calls for an asterisk [*|] for non-chord markings to be formatted as chords:
https://www.chordpro.org/chordpro/chordpro-chords/
Looks like I need to do some global search-and-replace on a whole bunch of files!