Have you looked at
perlop and
perlre? Those are,
probably, the definitive sources on the regex switches
and options. You might also take a look at Jeffrey
Friedl's book,
Mastering Regular Expressions. It's a bit outdated now, since there's
been a lot of new regex functionality added since the book
was published; but it's still a good source.
By the way: the possible switches for the tr operator
are
tr//cds