src/Zend/Filter/Inflector.php
public function setFilterRule($spec, $ruleSet)
    {
        $spec = $this->_normalizeSpec($spec);
        $this->_rules[$spec] = array();
        return $this->addFilterRule($spec, $ruleSet);
    }
public function setFilterRule($spec, $ruleSet)
    {
        $spec = $this->_normalizeSpec($spec);
        $this->_rules[$spec] = array();
        return $this->addFilterRule($spec, $ruleSet);
    }
Set a filtering rule for a spec.  $ruleSet can be a string, Filter object
or an array of strings or filter objects.

@param string $spec
@param array|string|Zend_Filter_Interface $ruleSet
@return Zend_Filter_Inflector