src/PEAR/ErrorStack.php
function setContextCallback($contextCallback)
    {
        if ($contextCallback === null) {
            return $this->_contextCallback = false;
        }
        if (!$contextCallback) {
            $this->_contextCallback = array(&$this, 'getFileLine');
        } else {
            if (is_callable($contextCallback)) {
                $this->_contextCallback = $contextCallback;
            }
        }
    }
function setContextCallback($contextCallback)
    {
        if ($contextCallback === null) {
            return $this->_contextCallback = false;
        }
        if (!$contextCallback) {
            $this->_contextCallback = array(&$this, 'getFileLine');
        } else {
            if (is_callable($contextCallback)) {
                $this->_contextCallback = $contextCallback;
            }
        }
    }
Set a callback that generates context information (location of error) for an error stack

This method sets the callback that can be used to generate context
information for an error.  Passing in NULL will disable context generation
and remove the expensive call to debug_backtrace()
@param array|string|null Callback function/method