src/PEAR/ErrorStack.php
function setDefaultCallback($callback = false, $package = false)
    {
        if (!is_callable($callback)) {
            $callback = false;
        }
        $package = $package ? $package : '*';
        $GLOBALS['_PEAR_ERRORSTACK_DEFAULT_CALLBACK'][$package] = $callback;
    }
function setDefaultCallback($callback = false, $package = false)
    {
        if (!is_callable($callback)) {
            $callback = false;
        }
        $package = $package ? $package : '*';
        $GLOBALS['_PEAR_ERRORSTACK_DEFAULT_CALLBACK'][$package] = $callback;
    }
Sets a default callback to be used by all error stacks

This method sets the callback that can be used to generate error
messages for a singleton
@param array|string Callback function/method
@param string Package name, or false for all packages
@static