http://stackoverflow.com/questions/6363397/how-to-tell-if-on...

As soon as you have backtracking and capture groups it's not a regular expression in the mathematical sense. These features make regexes more useful in many simple cases at the cost of making them harder to reason about in more difficult cases.

You know, I have. In some ways it is like communicating across cultures in that the question does not seem to make all that much sense to them. That I can tell, they don't ever search for patterns. The would look for that feature in their GUI log reading program, I suppose.

Failing that, they would write code, 100% in Java I think, and I suppose that if they had to do what I would reach for a regex to do, they would write code to do it. (Is this what jwz means by "Now they have two problems," that they should do the job in code?)

But, again, I don't think there is a real communication there. I'm not too sure what they mean and they look like they do not recognize the situations I ask about.

He gave a talk about all this which can be found here: https://vimeo.com/1485123

So he basically realized people were hacking regular expressions to get more power. So rather than playing that game, he climbed up a level on the automata ladder to get a more mathematically sound approach to the problem.