An XML document has an information set if it is well-formed and satisfies the namespace constraints.
There is no requirement for an XML document to be valid in order to have an information set.
[4] Infoset augmentation is somewhat controversial, with claims that it is a violation of modularity and tends to cause interoperability problems, since applications get different information depending on whether or not validation has been performed.
[5] Infoset augmentation is supported by XML Schema but not RELAX NG.
[6] There are also serialization formats for Binary XML, CSV,[7] and JSON.