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 http://www.w3.org/TR/xslt and http://www.w3.org/TR/xpath, 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:

• Saxon will automatically treat a result tree fragment as a node-set when required.

• Saxon supports the xsl:principal-result-document and xsl:result-document elements defined in the draft XSLT 2.0 specification, together with named xsl:output declarations.

• Saxon supports the use of xml:base to define the Base URI of a node, as defined in the XSLT 1.1 specifications, except in the case of the base URI of a processing instruction contained in an external entity. (This feature is supported regardless of the setting of [xsl:]version)

• The separator attribute on xsl:value-of and xsl:copy-of is implemented.

• The xsl:for-each-group instruction is implemented, together with the current-group() function.

• Named sort keys (using the xsl:sort-key declaration) are implemented, together with the sort() function that uses them.

• The collation attribute in xsl:sort is implemented, supported by a new saxon:collation declaration to manage collation names.

• The xsl:function declaration is implemented.

• Instructions such as xsl:for-each and xsl:copy-of can handle arbitrary sequences.

• The method="xhtml" attribute on the xsl:output declaration is implemented.

• The xsl:analyze-string instruction is available for regular expression processing.

• Variables and parameters may take an optional type attribute, defining the data type of the variable.

• A template rule can apply to several modes.

• The value of an enclosed expression in an attribute value template may be a sequence; the items in the sequence are output using space as a separator (this is not backwards compatible with XSLT 1.0

• The disable-output-escaping attribute of xsl:attribute is implemented

• The unparsed-text() function is implemented.

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:

• Saxon supports the following simple data types: string, boolean, decimal, duration, integer, float, double, date, dateTime, time, with their literal forms and constructors. All built-in subtypes of integer are also implemented (but note, unsignedLong does not support values greater than the maximum value of a Long). All built-in types derived by restriction from xs:string are implemented (but not the list types IDREFS, NMTOKENS, and ENTITIES).

• Sequences (of nodes or simple values) are supported. The sequence constructor (a, b, c) is implemented. Range expressions (a to b) are implemented.

• The "for", "if, "some", and "every" expressions are implemented.

• The operators except, intersect, union are implemented.

• Any expression may now appear on the right-hand side of the "/" operator (a run-time error is reported if it doesn't evaluate to a sequence of nodes).

• The operators is, isnot, <<, >gt; are implemented.

• The operators eq, ne, lt, gt, le, and ge are implemented.

• The idiv operator for integer division is implemented.

• The + and - operators may be used to add or subtract two durations of the same type. The * and div operators may be used to multiply or divide a duration by a number. (Subtraction of two dates to yield a duration, and addition of a date to a duration, are not yet implemented).

• In addition to functions defined in XPath 1.0 and XSLT 1.0, the following functions are available: avg(), base-uri(), compare(), context-item(), current-date(), current-dateTime(), current-group(), current-time(), dayTimeDuration-from-seconds(), deep-equal(), distinct-nodes(), duration(), empty(), exists(), find(), index-of(), insert(), lower-case(), matches(), max(), min(), node-kind(), remove(), replace(), root(), sequence-deep-equal(), sequence-node-equal(), string-pad(), subsequence(), time(), tokenize(), unparsed-text() [both arguments must be supplied], upper-case(), yearMonthDuration-from-months()

• The component extraction functions, get-X-from-Y, for types date, dateTime, time, and duration are also available. In the case of durations, they are named get-x-from-duration(), not get-x-from-yearMonthDuration() or get-x-from-dayTimeDuration().

  Note that in the dateTime and time data types, the timezone is retained as part of the value. Equality and ordering is done by normalizing the time to UTC, but conversion to a string, and extraction of components, reflects the timezone as originally specified.

  Constructor functions are available in both the schema-defined namespaces "http://www.w3.org/2001/XMLSchema" (conventional prefix xs) and "http://www.w3.org/2001/XMLSchema-datatypes" (conventional prefix xsd). They are available for all the built-in data types that have been implemented. The semantics are the same as a cast, that is, xs:dateTime($x) means exactly the same as cast as xs:dateTime($x).

  Ordering is implemented as a total order over all durations, based on the average length of a month (one year = 365.242199 days).

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.

Limitations

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

• XML Schema support, and constructs involving data types (for example, instance ofcast as, and the type attribute of xsl:variable)

• Derived simple types (e.g. xsd:short), with the exception of xsd:integer

• Primitive types other than those listed above, for example base64, binHex, anyURI, etc.

• Functions and operators other than those listed above.

• Handling of an empty sequence () as an argument to operators and functions.

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.

Documentation

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 java.net.URL 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:

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

Extensions

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
US-ASCII, ASCII 
UTF-8, UTF8
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.

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.

Michael H. Kay
27 August 2002