There are two. K = Keep, as in, "keep everything we've just matched", because I envision it being used in substitutions. The other mnemonic is "\K isn't used by anything yet". ;)

_____________________________________________________
Jeff[japhy]Pinyan: Perl, regex, and perl hacker, who'd like a job (NYC-area)
s++=END;++y(;-P)}y js++=;shajsj<++y(p-q)}?print:??;