A zero-width positive lookbehind assertion. For example, C</(?<=\t)\w+/>
matches a word that follows a tab, without including the tab in C<$&>.
-Works only for fixed-width lookbehind.
+Works only for fixed-width lookbehind of up to 255 characters.
There is a special form of this construct, called C<\K> (available since
Perl 5.10.0), which causes the
A zero-width negative lookbehind assertion. For example C</(?<!bar)foo/>
matches any occurrence of "foo" that does not follow "bar". Works
-only for fixed-width lookbehind.
+only for fixed-width lookbehind of up to 255 characters.
The alphabetic forms are experimental; using them yields a warning in the
C<experimental::alpha_assertions> category.