[sciurius]

Is "customgroup" an official ChordPro thing

No, but meta items must be single names. Otherwise it would not be possible to distinguish meta "foo" having value "bar boo" and meta "foo bar" having value "boo". Both would be written the same way:

Code:

{meta: foo bar boo}

A future version of the ChordPro specification may introduce quote handling.

One more: does the number of text file lines taken up with all the {} directives and such affect the resulting layout? I think I've figured out that blank lines in the .CHO file DO affect that layout,

That is correct.

so I'm just wondering whether metadata lines are ignored for page spacing or treated like blank lines.

Lines that contain a directive (that should be alone on the line) should be ignored w.r.t. formatting.

If the latter, are they allowed to be shoved together on the same line of the .CHO file?

No, but as I wrote above, this would not be necessary.