Do not fear! An hour of hacking solves the problem. Attached is a script that goes through the HTML version of the Lua manual and extracts documentation relevant to functions by name (and more besides). Some examples you can try include
luahelp luahelp gettable luahelp expressions luahelp metatableand much more besides. For guidance, run the script with no arguments.
Be warned that you will need to edit two variables! The script needs to know where the manual is, and it needs a pager that can display HTML read from standard input. The defaults should work on Debian linux, provided you have lynx installed.
The [luahelp script] is in the "insecure area" of this Wiki.