$hop =~ s/(r(eg)e(xp)/mutilate($1,$2)/eg

##</code><code>##

while ($hop =~ m/r(eg)e(xp)/g) {
	// handle stuff
	// to replace, substr($hop,length $`,length $&) = $replace; and think about slowness of $`, $& and all
	// to rewind, pos($hop)=$location;
}