$ perl -Mre=eval -e '/ (??{ "(?{1})" }) $_ /x'
Eval-group not allowed at runtime, use re 'eval' in regex m/(?{1})/ at -e line 1.

##</code><code>##

$ perl  -e '/ (?{1}) $_ /x'
Eval-group not allowed at runtime, use re 'eval' in regex m/ (?{1})  / at -e line 1.

$ perl -Mre=eval -e '/ (?{1}) $_ /x'

# This is the odd one
$ perl -Mre=eval -e '/ (??{ "(?{1})" }) $_ /x'
Eval-group not allowed at runtime, use re 'eval' in regex m/(?{1})/ at -e line 1.

$ perl -Mre=eval -e '/ (??{ qr"(?{1})" }) $_ /x'