(PHP 4 >= 4.0.5)preg_replace_callback -- Perform a regular expression search and replace using a callback
The behavior of this function is almost identical to preg_replace(), except for the fact that instead of replacement parameter, once should specify a callback that will be called and passed an array of matched elements in the subject string. The callback should return the replacement string. This function was added in PHP 4.0.5.
See also preg_replace().