Plain ASD-Files (System-Definition-Files for ASDF based Systems) are Lisp source-files with an .asd ending. There was a discussion on c.l.l a while ago, that it might be an idea to add a header-file that just contains meta-data.
R.P. Goldman proposed to use an external header format. In the same thread I (JochenSchmidt) proposed using a simple s-expression based header format.
The idea is that such a thing would be:
- smaller than the .asd file
- not contain arbitrary Lisp code (you need just READ)
- a solution to the problem what .asd file should be the one for ASDF Install