typos (x- instead of x--), comparing a non-pointer with NULL and so on. (I only actually sat down and read it recently, alas)
That's source, not metadata.
Ok, so what is metadata in this case?
Probably the information contained in the README and INSTALL files... what it needs to compile, what it needs to run, what makes it nicer to use, etc. Look at Debian's package control files: not perfect, but quite a lot better than most others available now.
With pkgsrc/ports, dependancies as well as limits on what it will work on (operating system and architecture - pkgsrc from NetBSD is meant to work with solaris and linux as well as all NetBSD archs unless there is a binary constraint.) are in the packages toplevel makefile, this also contains information such as where to find the package, it's homepage, licensing, etc. Extra features (such as whether to compile in gtk, ssl, etc support) can be controlled by /etc/mk.conf.
encap has no such system, but I've not really required it.