ZCML File
configure.zcml

<configure
    xmlns="http://namespaces.zope.org/zope"
    xmlns:apidoc="http://namespaces.zope.org/apidoc"
    xmlns:zcml="http://namespaces.zope.org/zcml"
    i18n_domain="zope"
    >
<adapter
    factory=".persistent.KeyReferenceToPersistent"
    for="persistent.interfaces.IPersistent"
    trusted="y"
    />
<class
    class=".persistent.KeyReferenceToPersistent"
    >
<require
    permission="zope.Public"
    interface=".interfaces.IKeyReference"
    />
</class>
<adapter
    factory=".persistent.connectionOfPersistent"
    for="persistent.interfaces.IPersistent"
    />
<configure
    zcml:condition="have apidoc"
    >
<apidoc:bookchapter
    id="keyref"
    title="Persistent Key References"
    doc_path="persistent.txt"
    />
</configure>
</configure>