All in the XML family

What is XML processing? Apart from the philosophical issues of syntax vs. serialization, documents vs. data, URIs vs. strings, etc., it isn't clear any more what an "XML application" looks like. It might just be XML 1.0, it might be XML 1.0 + Namespaces, XML 1.0 + Namespaces + XInclude + XML Base + XML Schemas + XSLT + XLink.
Is it a document or an Infoset? A spec called the "XML Information Set", or Infoset for short, describes the contents of an XML document that has also undergone namespace processing. This level of abstraction is adding complexity (and new names for old things) to specs, and "Infoset Contributions", like entities and defaulted attributes are now more controversial than they were. Generally speaking, any spec that makes an Infoset contribution may cause interoperability failures with systems not supporting that spec fully.
How about XLink, XML Base, XPointer, the Document Object Model, XInclude... The list of acronyms is ever-growing, and making the 'Semantic Web' work may require RDF (Resource Description Format), a sophisticated understanding of URIs, and ever more tools in the box...