- var_dump: documentation ( source)
- preg_split: documentation ( source)
<?php
$subject = <<<HTML
<div class="tabs_container">
<ul class="tabs">
##BEGINLOOP##gAs##
<li><a href="#">##title##</a></li>
##ENDLOOP##
</ul>
##BEGINLOOP##LI##
<div class="tabs_content">##title## is ##content##</div>
##ENDLOOP##
</div>
HTML;
$parts = preg_split('/(?:##BEGINLOOP##)([a-zA-Z]*)##(.+?)(?:##ENDLOOP##)/s', $subject, -1, PREG_SPLIT_DELIM_CAPTURE);
var_dump($parts);