=over

=item ${^RE_COMPILE_RECURSION_LIMIT}
X<${^RE_COMPILE_RECURSION_LIMIT}>

The current value giving the maximum number of open but unclosed
parenthetical groups there may be at any point during a regular
expression compilation.  The default is currently 1000 nested groups.
You may adjust it depending on your needs and the amount of memory
available.

This variable was added in Perl v5.30.0.

=back