[Drup]

I disagree with the sibling comments: regular expressions should still be about regular languages. It's not because Larry Wall committed yet another atrocity that we should all follow him off the cliff. Perl can keep its monster.

However, that doesn't mean we shouldn't strive for richer feature (within the confine of regularity), or that a parsing library automatically does the job better.

For instance: intersection and complement are regular operators that works very well in regular expressions. lookahead is a regular operator (lookbehind and backreferences are not), etc. Those operators do not necessarily work at all in richer parsing libraries. When added to regular expressions, they should be well handled and optimized by regex engines (which is is currently not the case). There's still work to do, features to add, which require appropriate testing techniques.

[eru]

Indeed, that's my opinion as well.

Regular languages are closed under a host of more interesting operations than those that have 'grown with the capabilities of our pattern matching engines'.