<? ob_start(); ?>

Apache does NOT get this stuff : PHP is buffering it


<? //apache does NOT parse this "< ?", PHP stops output buffering and continue php code interpretation

//php parses ....

?>PHP parses "? >", and does NOT send the following code to apache ... instead, PHP buffers it


xhtml ...


<? //apache still does NOT parse this "< ?", PHP parser stops buffering and interpret the following code

//php parses ....

echo od_get_contents(); //Now, php outputs the buffered content to apache

ob_end_clean(); //cleans the buffer
?>