Comment lines can start with #

[rddunphy]

Apparently leading whitespace is ignored, too.

[alerque]

You may well be right, but do you have any references to upstream documentation or perhaps the actual implementation code that backs up this assertion?

[rddunphy]

I'm actually not sure if there is any documentation, but it's mentioned in a couple of comments (e.g. here). The relevant code is at the end of config_rc.ts:

return excmds.filter(
	x =>
		/\S/.test(x) &&
		!x.trim().startsWith('"') &&
		!x.trim().startsWith("#"),
)

[alerque]

Thanks for tracking that down.