ZCML File
configure.zcml

<configure
    xmlns="http://namespaces.zope.org/zope"
    xmlns:browser="http://namespaces.zope.org/browser"
    i18n_domain="zope"
    >
<browser:page
    class=".browser.ExternalEditor"
    for="zope.app.externaleditor.interfaces.IExternallyEditable"
    permission="zope.View"
    name="external_edit"
    menu="zmi_views"
    title="External Edit"
    />
<class
    class="zope.app.file.File"
    >
</class>
</configure>