regex - php preg_split expression raises warning -

one of regular expressions raises warnings , can't figure out why or how change expression works fine. have escape anything? if yes, why , how? better understand...

$output = preg_split("/($begindelimiter|$enddelimiter)/", $text); 

php warning: preg_split(): compilation failed: missing ) @ offset 15 in /home/tim/importer.php on line 539

thanks help!

edit: $begindelimiter contains srf53 $enddelimiter contains (

the second 1 must problem, understand... needs escaped.

use preg_quote, variables contains special characters need escaped in regex.

preg_quote() takes string , puts backslash in front of every character part of regular expression syntax. useful if have run-time string need match in text , string may contain special regex characters.

$output = preg_split("/(".preg_quote($begindelimiter)."|".preg_quote($enddelimiter)."/", $text);