XInclude is a mechanism that allows you to aggregate several standalone XML documents into your document. In general XInclude is very similar to external entities , but there are two major differences:
External entities are not self-contained. Within an external entity it is not possible to define DOCTYPE as well as local internal or external entities.
External entities are always included as a whole. In contrast, when xincluding you may merge only a portion of the xincluded document (referenced by XPointer).
See XInclude Support for more details on the XInclude standard support.