Although having previously reached Last Call stage a year ago, the XML Core Working group have decided to publish another Working Draft of the XML Infoset, due to extensive reworking after feedback from the Last Call draft.
The Infoset specification describes an abstract data set of information items (the "document" information item, the "element" information item, etc.) which may be referenced by other XML specifications. It is important to understand that not all XML 1.0 documents have an Infoset (ones which don't conform to the XML Namespaces specification, for instance) and neither does the Infoset comprehensively catalog all an application might want to know about a document.
Apart from its utility in defining exactly which information items makes up a document for the sake of other specifications, the Infoset spec can aid application or API developers in establishing expectations about which data items they require/provide.
Released, rather poetically, exactly one year after the Last Call, the new draft includes many clarifications over the previous one, including appendices containing an example and a rather helpful "What is not in the Information Set".