1.
possible switches are: igSmxUs
The S means strip color codes (like using $strip($1-) as input text), the others are pcre switches. Best suggestion is to read http://www.pcre.org/pcre.txt a few times, there's useful regex info in there (somewhere).

The pcre switches (not the S) can even be set using (?i) and unset using (?-i)

2. Might be helpful to use {1,4} constructs, which would need some $chr(44) work in a $regex(). Ofcourse only an isre, no case sensitive versions...
(While we're at it, why no %var =~ /regex/ ? grin )

3. Can have it's uses, is asked before (a lot), problem is the alternative is too easy to do any work for it frown