Acabo de encontrar por casualidad las restricciones de javascript en cuanto a expresiones regulares se refiere:
Cita:
Iniciado por http://safari.oreilly.com/0596529376/I__CHP_9 * Decent Unicode support. Though Unicode characters can be matched and inserted, the \w word-character wildcard doesn't match anything outside the standard ASCII range. The same holds for the character classes [A-Z] and [a-z], so it is cumbersome to test whether or not a character is a letter or whether it's an upper or lower case. A real pain.
* Lookbehind, neither positive nor negative lookbehind. Very unfortunate.
* If–then constructs. Some script languages permit conditional statements; JavaScript does not. Would be useful.
* Named captures. Not a really great loss.
* Embedded comments. Not a big loss either.
Así que nos quedamos con lo importante: no lookbehind y no condicionales
