The i4i Patent 5,787,449 describes a document format and a method of encoding where the document content "is totally unstructured and has no embedded metacodes in the data stream." It further states that the document structure definition is described in a separate "metacode map" where "for each metacode applied to the content an entry in the metacode map is created which describes the metacode and gives its position."
On the other hand, "XML (Extensible Markup Language) is a way of marking up structured documents, that is, documents in which the markup primarily indicates the content's purpose rather than its formatting." Although, the content formatting description is stored separately from the structured content, the formatting description does not have to exist at all --- the document interpretation can be based solely on the XML tags which state the content's purpose.
Anyhow, similarities between XML and i4i patented method exist, but the differences are clear. XML document content is structured and mixed-up with markup tags, while i4i format explicitly states the document content "is totally unstructured" and stored in the "raw content area."
Therefore, the i4i patent does not affect XML format at all, if affects non-XML specific proprietary extensions Microsoft uses in the XML-based MS Office document format(s). These are the proprietary extensions Microsoft "invented" to screw-up other software developers who may try to develop open/save procedures for Microsoft proprietary "custom XML" documents. Well, I guess the chickens have come home to roost.