Some code for this is available in the extended CHM generator. The
problem is that you need a complete list of built in functions for that
to work in memory (or you need to check if a file exists which documents
that function) runtime. The second option should not be selected, since
we made our best possible to eliminate file_exists() checks from the
website code, and we do a lot... The first option means that the website
code should have a list of all the functions somewhere in memory for all
the page requests. And that list should be generated and populated somehow to all mirrors...
This list is generated to file funclist.txt by scripts/genfunclist.sh.
Well, that list of the list of functions implemented in PHP, and not the list of functions documented in the manual. Therefore it is not correct for linking stuff, since you might link to something which is not (yet) documented.
Goba