src/Zend/Filter/Callback.php
public function setCallback($callback, $options = null)
    {
        if (!is_callable($callback)) {

            throw new Zend_Filter_Exception('Callback can not be accessed');
        }

        $this->_callback = $callback;
        $this->setOptions($options);
        return $this;
    }
public function setCallback($callback, $options = null)
    {
        if (!is_callable($callback)) {

            throw new Zend_Filter_Exception('Callback can not be accessed');
        }

        $this->_callback = $callback;
        $this->setOptions($options);
        return $this;
    }
Sets a new callback for this filter

@param unknown_type $callback
@return unknown