./qr_test.pl atuvwz 'qr/ ( a )  (?| x ( y ) z | (p (q) r) | (t) u (v) (w) ) ( z ) /x'
qr=(?x-ism: ( a )  (?| x ( y ) z | (p (q) r) | (t) u (v) (w) ) ( z ) )
string=atuvwz
(?x-ism: ( a )  (?| x ( y ) z | (p (q) r) | (t) u (v) (w) ) ( z ) ) present
1=a
2=t
3=v
4=z