Help with preg_replace() , PLEASE

I'm going mad about this. Now, i've got the following text: --------------------------------- BEGIN TEXT ------------------------------ Let's see a very simple class sample <? class CTest { var $variable1; //Propiedad function DoThing() //Método { echo "esto es una prueba de clase"; echo "una clase es mejor que nada"; } } ?> And this was the sample ---------------------- END TEXT ------------------------------------------- I'm using preg_replace() to replace the PHP code qith the result of doing a highlight_string() to it. So i use this code: preg_replace("/(.*)(<\?.*?\?>)(.*)/imse","'\\1'.highlight_string('\\2').'\\3 '",$text); It ouputs this: <? class CTest { var $variable1; //Propiedad function DoThing() //Método { echo 'esto es una prueba de clase'; echo 'una clase es mejor que nada'; } } ?> In colored code, as you might see. and the weirdest of all: when i use this code: preg_replace("/(.*)(<\?.*?\?>)(.*)/imse","''.highlight_string('\\1').''.high light_string('\\2').''.highlight_string('\\3').''",$text); It recognizes the \\1 and \\3 strings!!!! Why can't i use then preg_replace("/(.*)(<\?.*?\?>)(.*)/imse","''.strtolower('\\1').''.highlight_ string('\\2').''.strtolower('\\3').''",$text]); or even a simpler preg_replace("/(.*)(<\?.*?\?>)(.*)/imse","'\\1'.highlight_string('\\2').'\\3 '",$text); I'm trying to separate the code from the rest of strings, as you might see. Can anyone help me? I got this far, and i feel it's a very silly thing, but i can't seem to be able to get it. Any ideas?