thanks - but i am just reading the codex ;-)
my motto: 'knowledges is knowing where it is written'
what i do quite often:
any time i come across something - a functions, or template tag, or whatever wordpress related:
i search the web for (like in this example, just for instance):
that should give you (apart from many other links) first of all the link to the documantation in the codex;
and a link to the core file (and the exact line):
there you get the line: defined at:
click on that link; that leads you to:
with a list of some functions; click on the title of the one you are looking up:
that leads you to here:
in there in line 851, you have it:
851 if ( !(is_single() || is_page() || $withcomments) || empty($post) )
also great for finding related functions, global wordpress variables, and expanding the vocabulary of wordpress terms...