ERRATUM:
File doc/HACKING erroneously points to http://lxr.sourceforge.net/lxr_internal_doc which is supposed to display LXR embedded documentation.
This information is in fact available at http://lxr.sourceforge.net/lxr_inline_doc.
If you read this page, automatic redirection did not work. Click on the preceding link to warp to the documentation page.