Yes, qr// does provide some problems here. But actually post processing the regex isnt a problem, as in principle thats exactly what I want to do. The objective is to turn patterns of the type (LIST|OF|LISTS) into a trie or DFA depending on the circumstances. If this is to be a silent optimisation then scanning the regex once its compiled will become necessary to identify points in the pattern where its possible. OTOH, introducing a new (?...:) type would reduce the costs involved, but would only make the optimisations available to new code. But this thread has given me lots of angles to consider. Thanks all.