# Saxon and XML 1.1

XML 1.1 (with XML Namespaces 1.1) extends XML 1.0 in three ways:

- The set of valid characters is increased

- The set of characters allowed in XML Names is increased

- Namespace undeclarations are permitted.

Saxon is capable of working with XML 1.1 input documents. If you want to use Saxon with XML 1.1, you should set the option "-xmlversion:1.1" on the Saxon command line, or call the method `configuration.setXMLVersion(Configuration.XML11)` or, in the case of XSLT, `transformerFactory.setAttribute(FeaturesKeys.XML_VERSION, "1.1")`

This configuration setting affects:

- validation of names used in XQuery and XPath expressions, including names of elements, attributes, functions, variables, and types

- validation of names of constructed elements, attributes, and processing instructions in XQuery and XSLT

- schema validation of values of type `xs:NCName`, `xs:QName`, `xs:NOTATION`, and `xs:ID`

- the permitted names of stylesheet objects such as keys, templates, decimal-formats, output declarations, and output methods

- the characters considered valid in the source of an XQuery query

- the characters considered valid in the result of the functions `codepoints-to-string()` and `unparsed-text()`

- the characters considered valid in the result of certain Saxon extension functions

- the way in which line endings in XQuery queries are normalized

- the default version used by the serializer (with output method XML)

Note that if you use the default setting of "1.0", then supplying an XML 1.1 source document as input may cause undefined errors.

It is advisable to use an XML parser that supports XML 1.1 when the configuration is set to "1.1", and an XML parser that does not support XML 1.1 when the configuration is set to "1.0". However, Saxon does not enforce this.

You can set the configuration to allow XML 1.1, but still serialize result documents as XML 1.0 by specifying the output property `version="1.0"`. In this case Saxon will check while serializing the document that it conforms to the XML 1.0 constraints (note that this check can be expensive). These checks are not performed if the configuration default is set to XML 1.0.

If you want the serializer to output namespace undeclarations, use the output property `undeclare-namespaces="yes"` as well as `version="1.1"`.

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