[wp-hackers] Changing two variables listed in apply_filters hook

[Ted Balaban]

I want to CHANGE the second variable.   In my corrected example
you return the first variable.   What do I specify as the return state-
ment?

A few simple questions.   Does the added filter function get inserted
at the apply_ filters statement?   Do the variables get changed at
the apply_filters statement and not before or after?   A function can
only be removed if a do_action is inserted in the function?  Finally
a function with do_action inserted can be processed first with low
priority with a user function and the primary function will not execute?

Beg my indulgence, I hope that is not too many questions but there is
no specific documentation in Codex except add_action and add_filter.