Is the KML Specification Complete?
KML version 2.2 is complete, but the KML specification is evolving and will be expanded under control of the Open Geospatial Consortium (OGC). Version numbers for KML have a double numbering system in the form of majorVersion.minorVersion. KML versions that have the same major version are guaranteed to be compatible with each other. The official definition of the KML syntax is contained in the KML schema, a formal XML definition of the language (see www.opengeospatial.org/standards/kml/). KML 2.2, the current version, is guaranteed to be supported by the schema for KML 2.3 when it is developed. See Appendix A for more information on KML versioning.
The best place to check for progress on future versions of KML is the OCG website (www.opengeospatial.org/standards/kml/). Companies such as Google and Microsoft, which offer free Earth browsers, also provide documentation on KML. The website for this book (www.informit.com/title/9780321525598) is updated periodically to provide you with current information on recent developments in KML.