Hie monks, I was playing around with look-ahead and look-behind, just stumbled upon this ,

my $str="axx12yya";
if($str=~m/12(?=.*a)/)
{
    print "match \n";
}
[download]

This matches the last 'a' in the string, Now I tried matching the first 'a' in the sting by look-behind assertion

my $str="axx12yya";

if($str=~m/12(?<=a.*)/)
{
    print "match \n";
}
[download]

I got an error message

Variable length lookbehind not implemented before HERE mark in regex m
+/12(?<=a.*
) << HERE / at test2.pl line 3.
[download]

Please explain why this error occurs and how to match the first occurrence of 'a'.One more thing noticed is if I replace the '.*' with \w{2} like
if($str=~m/12(?<=a\w{2})/)
I am not getting any error message but it fails to match.

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