[plt-scheme] doc.txt syntax

I've noticed that library documentation in doc.txt files obeys a
particular syntax.  I know that the ">" signifies a keyword entry for
use by Help Desk (documented in collects/help/doc.txt) but these lines
usually also include a type signature (for variables) or a pseudo-BNF
(for types).  Is the syntax for this annotation language documented
anywhere?  Is it parsed by any tools or is it just meant for human
consumption?  Are there tools to generate doc.txt files from source
code comments?

--dougo at place.org