#match context sensitive grammar --[0{N}1{N}2{N}] (012, 001122, 000111222, ...)
$h=qr/01|0(??{$h})1/;
$t=qr/12|1(??{$t})2/;
$cs=qr/(?=$h 2+$)(?=0+$t$)/x;

$init = "001122";
print "match\n" if ($init=~m/^$cs$/);