protected function indexRules(array $rules)
    {        
        $this->indexedRules = array();
        
        foreach($rules as $rule){
            if(isset($this->indexedRules[$rule[self::LOOKUP_CHAR]])){
                $this->indexedRules[$rule[self::LOOKUP_CHAR]][] = $rule;
            } else {
                $this->indexedRules[$rule[self::LOOKUP_CHAR]] = array($rule);
            }
        }       
    }