This looks like a bug - I will ask Cust Care to look here.

Looks like a manual update. There is no mention of this in the docs - i had to talk to many ppl to find this. I will log a doc bug to get this into the docs.

Another example -- Adobe Experience Manager Help | Invoking an Adobe Experience Manager Custom 6.4 Workflow from a web page

You can create your own servlets using the API. We have many HELPX artilces that show use of creating Sling Servlets - like this one: Adobe Experience Manager Help | Invoking an Adobe Experience Manager Custom 6.4 Workflow from a web page This Servlet invokes a Workflow - but it shows you how to cre...

A good place to start for digging deeper in this is here -- Home | CoralUI

After talking to an internal person - they stated -- I believe it is the cq:allowedTemplates property on /content/experience-fragments node that drives the availability of XF variations:

From your initial question - it seemed like you were having issue with using an Experience Fragment in your own project (AEM Site). This of course is solved by allowing the Experience Fragment component to be set in the policy of the editable template (assuming the page is based on the Editable Temp...

Looks like Adobe Social APIs are not part of your AEM code base. This error indicates that you bundle is looking in the OSGi service container and cannot find these Java packages. 

Nice response Arun!

As far as I know - Document Services are only applicable to J2EE AEM Forms and not migrated to the cloud. I will double check this.