=over

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

It is only guaranteed to return a defined value when the pattern was
executed with the C</p> modifier.

This is similar to C<$`> ($PREMATCH) except that to use it you must
use the C</p> modifier when executing the pattern, and it does not incur
the performance penalty associated with that variable.

See L</Performance issues> above.

This variable was added in Perl v5.10.0.

This variable is read-only, and its value is dynamically scoped.

=back