$ifmatch return the first part of the last conditional statement made.
Just like $v1 $v2 and $ifmatch2, this identifier return the value from the very last statement made:
This will echo 1 for $ifmatch because $test is evaluated before $ifmatch, so the $iif is the last statement made when $ifmatch evaluates.
Added: mIRC v5.4
Added on: 23 Jun 1998
Note: Unless otherwise stated, this was the date of original functionality.
Further enhancements may have been made in later versions.