It does , you just can't have space ... otherwise you couldn't distinguish between some constructs

Further to Anonymonk's point: This is common. Eliminating the extraneous space around  ? in the example below allows this pedestrian regex to compile and work as expected. 

>perl -wMstrict -le
"print 'match' if 'xxx' =~ m{ ( ? : x ) }xms;
"
Sequence (? ...) not recognized in regex...

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In reply to Re^2: Conditional regex by AnomalousMonk
in thread Conditional regex by 7stud

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