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after
Combined from primary sources listed below.

In Regexes§

See primary documentation in context for Lookbehind assertions

To check that a pattern appears after another pattern, use a lookbehind assertion via the after assertion. This has the form:

<?after pattern>

Therefore, to search for the string bar immediately preceded by the string foo, use the following regexp:

/ <?after foo> bar /

For example:

say "foobar" ~~ / <?after foo> bar /;   # OUTPUT: «bar␤»

However, if you want to search for a pattern which is not immediately preceded by some pattern, then you need to use a negative lookbehind assertion, this has the form:

<!after pattern>

Hence all occurrences of bar which do not have foo before them would be matched by

say "fotbar" ~~ / <!after foo> bar /;    # OUTPUT: «bar␤»

These are, as in the case of lookahead, zero-width assertions which do not consume characters, like here:

say "atfoobar" ~~ / (.**3) .**2 <?after foo> bar /;
# OUTPUT: «｢atfoobar｣␤ 0 => ｢atf｣␤»

where we capture the first 3 of the 5 characters before bar, but only if bar is preceded by foo. The fact that the assertion is zero-width allows us to use part of the characters in the assertion for capture.