/**
* Performs replacement of specified pattern and replacement strings.
* @param string $subject Text on which to perform replacement.
* @return string subject after replacement has been performed.
*/
public function replace($subject)
{
if ($this->pattern === null || $this->replace === null) {
throw new Exception("Missing pattern or replacement string regexp replace().");
}
return $this->engine->replace($this->pattern, $this->replace, $subject);
}
