User subdomain question

[aphenine]

I have a question that is driving me mad. I've been looking at the dreamwidth codebase folder, most of which is excellently described in a helpful wiki page. However, one thing I cannot for the love of anything work out is where the files are that are used when dreamwidth is is accessed through a user's subdomain or what controls the mapping.

So, for example, http://www.dreamwidth.org/userinfo.bml reads userinfo.bml in $LJHOME/htdocs. But if I am accessing http://aphenine.dreamwidth.org/read, then I'm not opening $LJHOME/htdocs/read. Same for tags and profile. Please could you tell me what mapping is being used and where is it defined?