The jury is still out on the /o modifier in perl 6, but it's not looking like it will be needed:
Several modifiers, /x, /s, and /m, are no longer needed and have been retired. It's unclear whether /o is necessary any more. We will assume it's gone unless it's shown that caching can't handle the problem. Note that the regex now has more control over when to cache subrules because it is no longer subject to the vagaries of standard interpolation.
The intelligent reader will judge for himself. Without examining the facts fully and fairly, there is no way of knowing whether vox populi is really vox dei, or merely vox asinorum. — Cyrus H. Gordon