push @stack, [ COMMENT => $1 ];
...
$stack[-1][0] eq 'COMMENT' and pop @stack for 1..3;


##</code><code>##

$ perl -le " $_ = qq{;banana\n;ro\n;sham\n;bo\n}; print; s{(?:^;[^\r\n]*[\r\n]+){1,3}\Z}{}m; print; "
;banana
;ro
;sham
;bo

;banana