William Allen Simpson wrote:
"Pointers to code would be appreciated." Where should I start looking?
After an hour or so looking, and discovering that the documentation at MediaWiki is woefully incomplete, but eventually finding a fairly useful page at http://meta.wikimedia.org/wiki/Categorylinks_table, it seems that "cl_to stores the name (excluding namespace prefix) of the desired category."
Without the namespace prefix, doesn't appear to be possible to have more than one namespace worth of categories, or categories that are specific to a single namespace.
Perhaps someday in the future, in conjunction with the unified username project, the user namespace could have its own categories and templates.
In the meantime, I'll just remind the disputing folks that there is currently no such thing as "encyclopedic" namespace and "non-encyclopedic" namespace. Categories and Templates apply to all namespaces.
Bits are bits are bits.