Using php to generate automatically a webpage can produce undesired empty rows (typically at the begging of your source code, before <!DOCTYPE html>).
To avoid them you could have i.g. to remove empty rows between ?> and <?php, that is something like the follow code:
?>
<?phpThe (new) working code should be
?>
<?php
On the contrary, empty rows inside <?php ... ?> blocks are not relevant.
In general, every empty (useless) row after a ?> could generate undesired empty rows in your html output source code.