ZCML File
subscribers.zcml

<configure
    xmlns="http://namespaces.zope.org/zope"
    xmlns:browser="http://namespaces.zope.org/browser"
    >
<subscriber
    handler=".catalog.indexAdded"
    for="
       .interfaces.ICatalogIndex
       zope.app.container.interfaces.IObjectAddedEvent
       "

    />
<subscriber
    handler=".catalog.indexDocSubscriber"
    for="zope.app.intid.interfaces.IIntIdAddedEvent"
    />
<subscriber
    handler=".catalog.reindexDocSubscriber"
    for="zope.lifecycleevent.interfaces.IObjectModifiedEvent"
    />
<subscriber
    handler=".catalog.unindexDocSubscriber"
    for="zope.app.intid.interfaces.IIntIdRemovedEvent"
    />
</configure>