It might be that the number of match attempts could be reduced by using such exotics as look-arounds in the regular expression, but there are surprisingly few people who really understand how to use those. The more complex the RE the more work the engine has to do to interogate it, so several simple REs might not be significantly slower than one complex RE - not to mention the chances of making a mistake which a complex expression brings.

Also note that the \G anchor might be in use, which indicates that the pattern starts when the previous global match left off.

A switch statement can be problematic with REs because the target can often match more than one 'case' (this can be an issue with korn shell case statements).