Have you noticed Variable-Length Lookbehinds: actually possible in Perl/PCRE!?

This is now history!

$ perl -wE 'say "aaaab" =~ /(?<=a{1,20})b/'
Variable length lookbehind not implemented in regex m/(?<=a{1,20})b/ a
+t -e line 1.
[$?: 255]
$ blead perl -wE 'say "aaaab" =~ /(?<=a{1,20})b/'
Variable length lookbehind is experimental in regex; marked by <-- HER
+E in m/(?<=a{1,20})b <-- HERE / at -e line 1.
1
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The original blog post by Tom Wyant here.