override email template model

Question

I am trying to override a function in Mage/Core/Model/Email/Template/Filter.php the module i wrote is just a config that looks like this

<?xml version="1.0"?>
<config>
    <modules>
        <Namespace_Module>
            <version>0.1.0</version>
        </Namespace_Module> 
    </modules>
    <global>
        <models>
            <module>
                <rewrite>
                    <email_template_filter>Namespace_Module_Model_Email_Template_Filter</email_template_filter>
                </rewrite>
            </module>
       </models>
    </global>
</config>

in Namespace/Module/Mage/Core/Model/Email/Template/Filter.php I have

<?php
class Namespace_Module_Model_Email_Template_Filter extends Mage_Core_Model_Email_Template_Filter
{...
    public function varDirective($construction)
    {

why is this not working?

Answer 1

I have done small mistake <module> should be <core>

Change from

 <global>
        <models>
            <module>
                <rewrite>
                    <email_template_filter>Namespace_Module_Model_Email_Template_Filter</email_template_filter>
                </rewrite>
            </module>
       </models>
    </global>

to

<global>
        <models>
            <core>
                <rewrite>
                    <email_template_filter>Namespace_Module_Model_Email_Template_Filter</email_template_filter>
                </rewrite>
            </core>
       </models>
    </global>