Saxon home page

Standards Conformance

XSLT 1.0 and XPath 1.0 conformance

Saxon XSLT implements the XSLT 1.0 and XPath 1.0 Recommendations from the World Wide Web Consortium, found at and, which are referred to here collectively as "XSLT"

Saxon is 100% conformant to the mandatory requirements of these recommendations, except in some cases where incompatibilities have been introduced in the XSLT 2.0 and XPath 2.0 working drafts.

XSLT 2.0 conformance

Saxon 7.1 implements many facilities defined in the draft XSLT 2.0 specification. This specification is not yet complete, and the facilities I have chosen to implement are those that appear to be the most stable.

The XSLT 2.0 features supported are as follows:

XPath 2.0 conformance

Saxon 7.1 implements many facilities defined in the draft XPath 2.0 specification.

The XPath 2.0 features supported are as follows:

Note, in replace(), if the pattern matches a zero-length string, each character in the source text is replaced by two instances of the replacement text. This is the Java behavior.

Conformance with other specifications

Saxon is dependant on the user-selected XML parser to ensure conformance with the XML 1.0 Recommendation and the XML Namespaces Recommendation.

Saxon implements the <?xml-stylesheet?> processing instruction as described in the W3C Recommendation Associating StyleSheets with XML Documents. The href pseudo-attribute must be a URI identifying an XML document containing a stylesheet, or a URI with a fragment identifier identifying an embedded stylesheet. The fragment must be the value of an ID attribute declared as such in the DTD.

Saxon works with any SAX2-conformant XML parser that is configured to enable namespace processing. There is one limitation: on the startElement() call from the XMLReader to the ContentHandler, the QName (that is, the third argument) must be present. According to the SAX2 specification, namespace-aware parsers are not obliged to supply this argument. However, all commonly-used parsers appear to do so.


Many aspects of XSLT 2.0 and XPath 2.0 are not yet implemented. These include:

There are many areas where the semantics implemented by Saxon still reflect the XPath 1.0 rules, for example the rules for conversion of numbers to strings. In some cases the XPath 2.0 rules in these areas are not yet stable (that is, there are open issues documented in the current working draft).

Other examples of facilities not yet implemented include: backwards compatibility mode; the xsl:import-schema declaration.


The XSLT specification says that the documentation for an implementation should specify which URI schemes are supported. Saxon supports the URI scheme implemented by the Java class, with the optional addition of a fragment identifier, as described below. Additionally, Saxon allows the user to nominate a URIResolver class which can be used to implement any URI scheme the user wants.

The XSLT specification says that the documentation for an implementation should specify for which media types fragment identifiers are supported. The standard URI resolver supports access to XML documents only. A simple fragment identifier is allowed, consisting of the value of an ID attribute in the document. The effect is to return the subdocument rooted at the element with this identifier if there is one, or an empty document otherwise. For example, the URI mydoc.xml#aaa locates the XML document mydoc.xml, and if it contains an element <eeee id="aaa">, where id is an attribute of type ID, then the document retrieved is an XML document with this <eeee> element as its outermost (document) element.

The values of the vendor-specific system properties are:

xsl:vendorSAXON n.n.n from Michael Kay

All these values are subject to change in future releases. Users wishing to test whether the processor is Saxon are advised to test whether the xsl:product system property has the value "SAXON".

The reason for returning 1.8 from xsl:version is that the product is not yet fully conformant with XSLT 2.0


Saxon implements a number of extensions to standard XSLT, following the rules for extension functions and extension elements where appropriate. The extensions are documented in extensions.html. They are all implemented in accordance with the provisions in the standard for extensibility.

Character encodings supported

The following is the list of encodings recognized by the built-in AElfred parser (case-insensitive):

ISO-8859-1, 8859_1, ISO8859_1
ISO-10646-UCS-2, UTF-16, UTF-16BE, UTF-16LE

The encodings available on output are the intersection of:

ascii, us-ascii, utf-8, utf8, utf-16, utf16, iso-8859-1, iso-8859-2
koi8-r, cp852, cp1250, windows-1250, cp1251, windows-1251
(again case-insensitive)

with whatever your Java VM supports.

If you select an encoding that the Java VM recognizes, but which is not in the above list, then the output will be written in the requested encoding, but all non-ASCII characters will be written as character references.

XML 1.0 Conformance

Saxon can be used with any SAX-conformant XML parser. The extent of XML conformance depends entirely on the chosen parser.

The default parser is a version of Ælfred. There is one known non-conformance in the version of the Ælfred parser provided with the Saxon product: it does not enforce the constraint that the contents of a general entity must be well-formed. Note, however, that this parser does not perform XML validation.

DOM Conformance

Saxon accepts input (both source document and stylesheet) from any standards-compliant DOM implementation.

Saxon allows the result tree to be attached to any Document or Element node of an existing DOM. Any DOM implementation can be used, provided it is mutable.

Saxon's internal tree structure (which is visible through the Java API, including the case where Java extensions functions are called from XPath expressions) conforms with the minimal requirements of the DOM level 2 core Java language binding. This DOM interface is read-only, so all attempts to call updating methods throw an appropriate DOM exception. No optional features are implemented. The DOM interfaces to Saxon's tree structure do not reveal namespace nodes as attributes. This means it is not possible to get information about namespace declarations except by calls such as getPrefix() and getNamespaceURI() on Element and Attr nodes).

If an extension function returns a DOM Node or NodeList, this must consist only of Nodes in a tree constructed using Saxon. Since Saxon's trees cannot be updated using DOM methods, this means that the nodes returned must either be nodes from the original source tree, or nodes from a tree constructed using Saxon's proprietary API. It is not possible to construct the tree using DOM methods such as createElement() and createAttribute().

JAXP 1.1 Conformance

Saxon implements the JAXP 1.1 API (including TrAX), as defined in JSR-63. Saxon implements the interfaces in the javax.xml.transform package in full, including support for SAX, DOM, and Stream input, and SAX, DOM, and Stream output.

There are restrictions in using transform() on a DOMSource when the node to be transformed is a node other than the root (i.e. the DOM Document node). These apply only if the supplied DOM is a third-party DOM, not if it is a Saxon-constructed tree. Specifically, if the start node is not the root then it must be an element; and it must not have an ancestor or preceding-sibling node, or an ancestor with a preceding-sibling node, that is an entity reference node or CDATA section node. In addition, the element must be part of a tree that is rooted at a Document node.

Saxon also implements the javax.xml.parsers API. The SAX interfaces are implemented in full. The DOM interfaces are limited by the capabilities of the Saxon DOM, specifically the fact that it is read-only. Nevertheless, the DocumentBuilder may be used to construct a Saxon tree, or to obtain an empty Document node which can be supplied in a DOMResult to hold the result of a transformation.

Error recovery policy

Where the XSLT specification requires that an error be signaled, Saxon produces an error message and terminates stylesheet execution. In the case of errors detected at compile time, it attempts to report as many errors as possible before terminating; in the case of run-time errors, it terminates after the first error.

Where the XSLT specification states that the processor may recover from an error, Saxon takes one of three actions as described in the table below. Either it signals the error and terminates execution, or it recovers silently from the error in the manner permitted by the specification, or it places the action under user control. In the latter case there are three options: report the error and terminate, recover silently, or (the default) recover after writing a warning to the system error output stream. These actions can be modified by supplying a user-defined ErrorListener.

Handling of individual recoverable errors is described in the table below.

There is more than one template rule that matches a node, with the same import precedence and priority User option
There is more that one xsl:namespace-alias statement for a given prefix, with the same import precedence Recover silently
An element name defined using xsl:element is invalid User option
An attribute name defined using xsl:attribute is invalid User option
There are several attribute sets with the same import precedence that define the same named attribute Recover silently
A processing-instruction name defined using xsl:processing-instruction is invalid User option
A node other than a text node is written to the result tree while instantiating xsl:attribute, xsl:comment, or xsl:processing-instruction User option
Invalid characters are written to the content of a comment or processing instruction User option
An attribute node or namespace node is written directly to the root of a result tree fragment, or to any other node that is not an element node. User option
The document() function identifies a resource that cannot be retrieved User option
There are several xsl:output elements specifying the same attribute with the same import precedence Recover silently
disable-output-escaping is used for a text node while instantiating xsl:attribute, xsl:comment, or xsl:processing-instruction Recover silently
disable-output-escaping is used for a text node within a result tree fragment that is subsequently converted to a string or number Recover silently
disable-output-escaping is used for a text node containing a character that cannot be output using the target encoding Recover silently

Michael H. Kay
27 August 2002