src/Zend/Filter/Word/SeparatorToSeparator.php
protected function _separatorToSeparatorFilter($value)
    {
        if ($this->_searchSeparator == null) {

            throw new Zend_Filter_Exception('You must provide a search separator for this filter to work.');
        }

        $this->setMatchPattern('#' . preg_quote($this->_searchSeparator, '#') . '#');
        $this->setReplacement($this->_replacementSeparator);
        return parent::filter($value);
    }
protected function _separatorToSeparatorFilter($value)
    {
        if ($this->_searchSeparator == null) {

            throw new Zend_Filter_Exception('You must provide a search separator for this filter to work.');
        }

        $this->setMatchPattern('#' . preg_quote($this->_searchSeparator, '#') . '#');
        $this->setReplacement($this->_replacementSeparator);
        return parent::filter($value);
    }
Do the real work, replaces the seperator to search for with the replacement seperator

Returns the replaced string

@param  string $value
@return string