Some regular expressions take a long time to match certain input strings
to the point where the time it takes to match a string of length n is
proportional to nk or even 2n. Such regular expressions can negatively
affect performance, or even allow a malicious user to perform a Denial
of Service ("DoS") attack by crafting an expensive input string for the
regular expression to match.

This replaces the problematic regular expression by a little parser that
checks for the same results as the regular expression.