It's a quite simple thing to do:
Copy the portion of the text before the text that you want, and call it $start. Do the same with the text right after it, and call it $end.
Then, get the whole block, and call it $mess 🙂
$res=preg_match("|$start(.*)$end|s", $mess, $regs);
Then $regs[1] will be the text between the two of 'em.
Dave