<? and <?php

[eluser]Ngulo[/eluser]
hi everyone, i'm new on this forum and new with CI,but i really enjoying it for me it's amazing this framework

i'm just trying to understand what's the meaning of short tags <? compared to the simple tag <?php

for example i'm using this code in a view.php:
[code][<?=form_open('Home','id="form"');?>
<?= form_close();?> /code]

and it's so funny but the question is,why if i use this other code it doesn't works?
[code][<?php=form_open('Home','id="form"');?>
<?php= form_close();?> /code]

maybe i didn't understand the meaning of <? short tag, can i use normal tags <?php ?

wich are the main differences between these two ? if my hoster does not support PHP short tags maybe it could be a problem?

thanks a lot and i think i will become a really "hot" CI fan

psorry for my bad english