This would really be helpful for creating REX expressions, since they are not fully compatible with GREP.
No there isn't. A couple rules of thumb that will help creating REX expressions:
rex -x will dump an English version of the expression if you have the full Texis product
It can be helpful to anchor the expression to ensure directionality, particularly when using negative expressions ( ! or [^ )
It is deterministic and greedy, it does not backtrack to complete a match.
Repetition operators apply to the string since the last repetition operator, not just the preceding character.