> For implementations that don't support it, skipping the thing is a
> one-line macro:

Also most source files are UTF-8 nowadays, and if UTF-8 is the
implementation's default encoding then no (declare-file ...) form is
needed in most files.

Putting these facts together, adoption could be very gradual. And
if/when we want a standard way to encode authorship, licensing,
dependencies, compiler and linker flags for FFI, etc. is desired, that
information could be added to the same form (when it applies on a file
scope instead of a library scope - in the later case the library and
define-library forms could be extended similarly).

It could be mandated that if a (coding ...) declaration is included, it
must be the very first thing declared. This might make the raw-byte
reader even simpler.