Use the lightning:availableForChatterExtensionComposer interface to integrate your custom
apps into the Chatter publisher and place the custom app’s payload in the feed. This
interface is available in Lightning communities.
The lightning:availableForChatterExtensionComposer interface
works with the lightning:availableForChatterExtensionRenderer interface and the lightning:sendChatterExtensionPayload event to integrate your
custom apps into the Chatter publisher and to render the app’s payload in the feed.