OK, there are actually four similar but different problems here:

- Text comment to be ignored: `; foo ...`

- S-expression comment to be ignored: `#; (foo bar ...)`

- S-expression metadata related to the entire file it's in: e.g. my
`declare-file` proposal

- S-expression metadata related to an ordinary non-meta-level
S-expression: e.g. https://clojure.org/reference/metadata

John's proposal of `#;;` would probably be file-level metadata, or a
more granular level. But probably not attached to a particular
non-meta-level sexp as the Clojure ^ thing is.