Every PHP developer know PHP tags is something like <?php ?>
but some developer use it like <? ?> so called PHP short tag. but its only available if enabled using the short_open_tag php.ini configuration file directive, or if PHP was configured with the –enable-short-tags option).
Using short tags( <? ) should be avoided when developing applications or libraries that are meant for redistribution, or deployment on PHP servers which are not under your control, because short tags may not be supported on the target server. For portable, redistributable code, be sure not to use short tags.