An attribute specifying, as part of the XML declaration, the version number of this document. If there is no declaration and if this document supports the "XML" feature, the value is "1.0" . If this document does not support the "XML" feature, the value is always null. Changing this attribute will affect methods that check for invalid characters in XML names. Application should invoke Document.normalizeDocument() in order to check for invalid characters in the Nodes that are already part of this Document.

DOM applications may use the DOMImplementation.hasFeature(feature, version) method with parameter values "XMLVersion" and "1.0" (respectively) to determine if an implementation supports [XML 1.0]. DOM applications may use the same method with parameter values "XMLVersion" and "1.1" (respectively) to determine if an implementation supports [XML 1.1]. In both cases, in order to support XML, an implementation must also support the "XML" feature defined in this specification. Document objects supporting a version of the "XMLVersion" feature must not raise a NOT_SUPPORTED_ERR exception for the same version number when using Document.xmlVersion.