Sometimes a filter tests if a given edit matches any values in a list (or a given regex) and if so, warns the user about it. In those cases it would be useful to be able to show the matched text as part of the warning message. Examples:
This edit introduces the template "$1", which was deprecated after consensus (...)
This edit contains the phrase "$1", which may be considered offensive (...)
This would help a lot reviewing filters due to false positives, because the matching text would be easily available directly in the message.