web pointers

Certain procmail rules are bizarre.  To match '$', I was forced to use
\\$ and only through trial and error did I locate that.  Is there a nice
web page that sums this kind of stuff up?  ie: operators, metacharacters,
etc.

The other thing I'm looking for is citations for the scoring rulesets,
how do I invoke various actions depending on the summation level?  Or am
I stuck with a not-so-useful true/false invoke/don't invoke setup?

-j