Interestingly I'd say a regular expression is absolutely not a DSL. It's sort of the opposite. A DSL is a tightly crafted interface for the configuration needed to support solutions to one somewhat unique problem. And the "trap" above is that the fact that the problem area is narrow means that only experts will really understand the DSL.

A regex is a tool implementing a solution (albeit a tightly crafted one) to an extremely broad set of problem areas. I mean, sure, in some sense it's a "DSL for string matching", but that doesn't really capture the essence of the DSL trap mentioned above. I mean, almost everyone needs string matching. So there's no trap: basically everyone knows regex syntax, even if they like to complain about it.