[racket-dev] pconvert and current-build-share-hook?

I'm having a little difficulty understanding the documentation of the
mzlib/pconvert library
(http://docs.racket-lang.org/mzlib/mzlib_pconvert.html)  In
particular, I'm trying to understand current-build-share-hook.

The description talks about using the basic-share and a sub-share
functions, but I don't know exactly what their roles are: I can not
tell from the documentation alone how to use them on a particular
structured value.  This is important to me because I'm trying to work
around a bug in the library
(http://bugs.racket-lang.org/query/?cmd=view&pr=12373).  I'm not
completely convinced that the workaround I'm offering
(https://github.com/dyoo/cs019-lang/commit/1f0a2ebb5775a97e6cd946672d24d31ed1e3927d)
is actually doing the right thing.