Provide client side API to manipulate ContentType XmlDocuments
As far as I know, there's no way to manipulate XmlDocuments collection of ContentType objects.
On server side, we can directly use SPContentType.XmlDocuments to manipulate the collection, but I didn't find any client side way to do this.
Neither CSOM, nor REST API nor Web service provide something able to reach my goal.
XmlDocuments collection is useful to store content type related configuration. There is OOB configuration like policies, or receivers stored in this collection, and some 3rd party data too (at least we are trying to).