Thanks, davido. You and ysth both hit on similar situations. I especially like the negated class (which ends up, in the regex engine being a many-valued class (I suspect...though I'm by no means that knowledgable of the regex engine).

In my response to ysth, I wondered why one wouldn't except the single engtry, programmatically built-up case and provide a more regex-engine-efficient cast in that instance. Your comment that:

...is simply one less thing to worry about.

makes good sense to me and is in the spirit of what a lot of Perl culture is all about.

I think I'd probably take the extra effort to check for the single entry and try to cast it as a special case; but that's just my compulsive nature.

Thanks, davido (and everyone) for your insights. You're all helping me to be a better monk.