> 1. Compatibility is a key factor here, so we'd want to go with base-level JSON. I'd prefer being able to have trailing commas in lists, but not enough to make life hard for someone implementing this without access to a JSON5 parser.

This is what I was referring to. This is not json:

> #..meta: format=json, length=270

> The header formats are meant to be very simple key/value pairs that are known by the parser, and not free-form bits of metadata. That's what the "meta" blocks are for. The parsing rules for the header are intentionally very simple.

Exactly my point. That level of flexibility for a .patch format to support another language embedded in it is overwhelming. Keep in mind that you are proposing a textual format, not a binary format. So people will use 3rd party text parsing tools to play with it. And having 2 distinct languages in there makes that annoying and a pain.