XML Information Set (XML Infoset) is a W3C specification describing an abstract data model of an XML document in terms of a set of information items. The definitions in the XML Information Set specification are meant to be used in other specifications that need to refer to the information in a well-formed XML document.
An information set can contain up to eleven different types of information items:
- The Document Information Item (always present)
- Element Information Items
- Attribute Information Items
- Processing Instruction Information Items
- Unexpanded Entity Reference Information Items
- Character Information Items
- Comment Information Items
- The Document Type Declaration Information Item
- Unparsed Entity Information Items
- Notation Information Items
- Namespace Information Items
XML was initially developed without a formal definition of its infoset. This was only formalised by later work beginning in 1999, first published as a separate W3C Working Draft at the end of December that year. Infoset recommendation Second Edition was adopted on 4 February, 2004. If a 2.0 version of the XML standard is ever published, it is likely that this would absorb the Infoset recommendation as an integral part of that standard.