This page describes the extension functions and extension elements supplied with the SAXON product.
If you want to implement your own extensions, see extensibility.html.
These extension functions and elements have been provided because there are things that are difficult to achieve, or inefficient, using standard XSLT facilities alone. As always, it is best to stick to standard if you possibly can: and most things are possible, even if it's not obvious at first sight.
| Before using a Saxon extension, check whether there is an equivalent EXSLT extension available. EXSLT extensions are more likely to be portable across XSLT processors. |
EXSLT is an initiative to define a standardized set of extension functions and extension elements that can be used across different XSLT processors.
Saxon now supports the EXSLT modules Common, Math, Sets, DatesAndTimes, and Functions. The full list of EXSLT extension functions implemented is:
Also the following functions in the dates-and-times module: date-time(), date(), time(), year(), leap-year(), month-in-year(), month-name(), month-abbreviation(), week-in-year(), week-in-month(), day-in-year(), day-in-month(), day-of-week-in-month(), day-in-week(), day-abbreviation(), hour-in-day(), minute-in-hour(), second-in-minute().
plus the following elements:
These have considerable overlap with extension function and elements that have previously been provided in the Saxon namespace. The Saxon versions of the functions remain available, for the time being, but the EXSLT versions are preferred.
An extension attribute is an extra attribute on an XSL-defined element. Following the rules of XSLT, such attributes must be in a non-default namespace. For SAXON extension elements, the namespace must be the SAXON namespace URI "http://icl.com/saxon"
For example, the saxon:trace attribute can be set as follows:
<xsl:template match="item" saxon:trace="yes"
xmlns:saxon="http://icl.com/saxon">
The extension attributes supplied with the SAXON product are as follows:
A number of additional attributes, or attribute values, are allowed on the xsl:output and xsl:document elements, beyond those defined in the XSLT 1.1 specification.
Like the standard attributes of xsl:output and xsl:document, these are all interpreted as attribute value templates.
The method attribute of xsl:output and xsl:document can take the standard values "xml", "html", or "text", or a QName.
If a QName is specified, the local name may be:
The prefix of the QName must correspond to a valid namespace URI. It is recommended to use the SAXON URI "http://icl.com/saxon", but this is not enforced.
Two additional attributes are available on the xsl:output and xsl:document
elements, for use when method="saxon:fop". (Note, these are not fully
tested).
fop:renderer="org.apache.fop.render.pdf.PDFRenderer".fop:configuration="c:\config\fop.xml"Here fop: is the prefix of a namespace whose URI must be
http://icl.com/saxon/fop
When the output is XML or HTML with indent="yes", the saxon:indent-spaces attribute may be used to control the amount of indentation. The value must be an integer.
This attribute allows greater control over how non-ASCII characters will be represented on output.
With method="xml", two values are supported: "decimal" and "hex". These control whether numeric character references are output in decimal or hexadecimal when the character is not available in the selected encoding.
With HTML, the value may hold two strings, separated by a semicolon. The first string defines how non-ASCII characters within the character encoding will be represented, the values being "native", "entity", "decimal", or "hex". The second string defines how characters outside the encoding will be represented, the values being "entity", "decimal", or "hex". Here "native" means output the character as itself; "entity" means use a defined entity reference (such as "é") if known; "decimal" and "hex" refer to numeric character references. For example "entity;decimal" (the default) means that with encoding="iso-8859-1", characters in the range 160-255 will be represented using standard HTML entity references, while Unicode characters above 255 will be represented as decimal character references.
This attribute may be set on the xsl:output element when method="html". The normal action of the HTML output method, as specified in the XSLT standard, is to generate a <META> tag immediately after the <HEAD> tag, containing details of the media type and character encoding. Setting this attribute to "yes" causes this output to be suppressed. Typical usage is
<xsl:output method="html" saxon:omit-meta-tag="yes">
The saxon:next-in-chain attribute is used to direct the output to another stylesheet. The value is the URL of a stylesheet that should be used to process the output stream. In this case the output stream must always be pure XML, and attributes that control the format of the output (e.g. method, cdata-section-elements, etc) will have no effect. The output of the second stylesheet will be directed to the destination that would have been used for the first stylesheet if no saxon:next-in-chain attribute were present: for xsl:output, this means the original transformation result destination; for xsl:document, it means the file specified by the href attribute.
Any number of user-defined attributes may be defined on both xsl:output and xsl:document. These attributes must have names in a non-null namespace, which must not be either the XSLT or the Saxon namespace. These attributes are interpreted as attribute value templates. The value of the attribute is inserted into the Properties object made available to the Emitter handling the output; they will be ignored by the standard output methods, but can supply arbitrary information to a user-defined output method. The name of the property will be the expanded name of the attribute in JAXP format, for example "{http://my-namespace/uri}local-name", and the value will be the value as given, after evaluation as an attribute value template.
A SAXON extension function is invoked using a name such as saxon:localname().
The saxon prefix (or whatever prefix you choose to use) must be associated with the SAXON namespace URI "http://icl.com/saxon" or (for backwards compatibility) any URI ending with "/com.icl.saxon.functions.Extensions".
For example, to invoke the node-set function, write:
<xsl:variable name="fragment">value</xsl:variable>
..
<xsl:apply-templates
select="saxon:node-set($fragment)"
mode="postprocess"
xmlns:saxon="http://icl.com/saxon"/>
The extension functions supplied with the SAXON product are as follows:
| after(node-set-1, node-set-2) | This returns a node-set that contains all the nodes in node-set-2 that follow (in document order) at least one node of node-set-2. If node-set-2 is empty, the function returns an empty set. This function corresponds to the XQuery AFTER operator and (approximately) to the EXSLT trailing() function. |
| before(node-set-1, node-set-2) | This returns a node-set that contains all the nodes in node-set-2 that precede (in document order) at least one node of node-set-2. If node-set-2 is empty, the function returns an empty set. This function corresponds to the XQuery BEFORE operator and (approximately) to the EXSLT leading() function. |
| closure(node-set, expression) | This returns a node-set obtained as the transitive closure of applying the given expression to each node in the supplied node-set. For example, saxon:closure(., saxon:expression('*')) returns all the descendant elements of the context node, and saxon:closure(., saxon:expression(id(@idref))) returns all the elements that can be reached by following the @idref attribute treating it as the ID of another element. The function does not detect cycles: if cycles are present in the data, it will recurse indefinitely until it runs out of stack space. To allow expressions such as "*[@father=current()/@name]", each time the expression is evaluated the current node is set to be the same as the context node. |
| difference(node-set-1, node-set-2) | This returns a node-set that is the difference of the two supplied node-sets, that is, it contains all the nodes that are in node-set-1 that are not also in node-set-2. This function is deprecated: use the EXSLT difference() function instead, for portability. |
| distinct(node-set-1, [stored-expression]) | This returns a node-set obtained by eliminating nodes in node-set-1 that have duplicate values for the supplied stored expression, evaluated as a string. A stored expression may be obtained as the result of calling the saxon:expression() function. If no stored expression is supplied, the default is expression('.'), that is, the string-value of the node. If several nodes produce the same string value, the one that is first in document order will be retained. The stored expression is evaluated for each node in node-set-1 in turn, with that node as the context node, with the context position equal to the position of that node in node-set-1, and with the context size equal to the size of node-set-1. Example: <xsl:for-each select="saxon:distinct(surname, saxon:expression('substring(.,1,1)')"> will process the first surname starting with each letter of the alphabet in turn. Note: for the single-argument version, the EXSLT distinct() function should be used in preference, for portability reasons. |
| eval(stored-expression) | This returns the result of evaluating the supplied stored expression. A stored expression may be obtained as the result of calling the saxon:expression() function. The stored expression is evaluated in the current context, that is, the context node is the current node, and the context position and context size are the same as the result of calling position() or last() respectively. Example: saxon:eval(saxon:expression(concat(2, $op, 2))) |
| evaluate(string) | The supplied string must contain an XPath expression. The result of the function is the result of evaluating the XPath expression. This is useful where an expression needs to be constructed at run-time or passed to the stylesheet as a parameter, for example where the sort key is determined dynamically. The context for the expression (e.g. which variables and namespaces are available) is exactly the same as if the expression were written explicitly at this point in the stylesheet. The function saxon:evaluate(string) is shorthand for saxon:eval(saxon:expression(string)). |
| exists(node-set-1, stored-expression) | This returns true if the supplied stored expression evaluates to true for some node in node-set-1, when evaluated as a boolean. Otherwise it returns false. A stored expression may be obtained as the result of calling the saxon:expression() function. The stored expression is evaluated for each node in node-set-1 in turn, with that node as the context node, with the context position equal to the position of that node in node-set-1, and with the context size equal to the size of node-set-1. Example: saxon:exists(sale, saxon:expression('@price * @qty > 1000')) will return true if the context node has a child <sale> element for which the product of price and qty exceeds 1000. |
| expression(string) | The supplied string must contain an XPath expression. The result of the function is a stored expression, which may be supplied as an argument to other extension functions such as saxon:eval(), saxon:sum() and saxon:distinct(). The result of the expression will usually depend on the current node. The expression may contain references to variables that are in scope at the point where saxon:expression() is called: these variables will be replaced in the stored expression with the values they take at the time saxon:expression() is called, not the values of the variables at the time the stored expression is evaluated. Similarly, if the expression contains namespace prefixes, these are interpreted in terms of the namespace declarations in scope at the point where the saxon:expression() function is called, not those in scope where the stored expression is evaluated. |
| for-all(node-set-1, stored-expression) | This returns true if the supplied stored expression evaluates to true for every node in node-set-1, when evaluated as a boolean. Otherwise it returns false. A stored expression may be obtained as the result of calling the saxon:expression() function. The stored expression is evaluated for each node in node-set-1 in turn, with that node as the context node, with the context position equal to the position of that node in node-set-1, and with the context size equal to the size of node-set-1. Example: saxon:forAll(sale, saxon:expression('@price * @qty > 1000')) will return true if for every child <sale> element of the context node, the product of price and qty exceeds 1000. |
| get-pseudo-attribute(string) | This function parses the contents of a processing instruction whose content follows the conventional attribute="value" structure (as defined for the <?xsl-stylesheet?> processing instruction). The context node should be a processing instruction; the function returns the value of the pseudo-attribute named in the first argument if it is present, or an empty string otherwise. |
| get-user-data(string) | This returns user data associated with the context node in the source document. The user data must be set up previously using the saxon:setUserData() function. |
| has-same-nodes(node-set-1, node-set-2) | This returns a boolean that is true if and only if node-set-1 and node-set-2 contain the same set of nodes. Note this is quite different from the "=" operator, which tests whether there is a pair of nodes with the same string-value. |
| highest(node-set-1 [, stored-expression]) | This returns (as a node-set) the node from node-set-1 that has the highest value of the supplied stored expression, evaluated as a number. If the stored expression is omitted, the expression "number(.)" is evaluated: that is, the string value of the node, converted to a number. A stored expression may be obtained as the result of calling the saxon:expression() function. The stored expression is evaluated for each node in node-set-1 in turn, with that node as the context node, with the context position equal to the position of that node in node-set-1, and with the context size equal to the size of node-set-1. Any NaN values are ignored. If the node-set is empty, the result is an empty node-set. If several nodes have the highest value, the result node-set contains the one that is first in document order. This differs from the EXSLT highest() function, which returns all the nodes that have the maximum value. Example: saxon:highest(sale, saxon:expression('@price * @qty')) will evaluate price times quantity for each child <sale> element, and return the node for which this has the highest value. |
| if(condition, value-1, value-2) | The first argument is evaluated as a boolean; if it is true, the function returns the value value-1, if it is false, it returns value-2. The value may be of any type. Both the second and third arguments are evaluated even though only one of the values is used. |
| if-null(java-object) | The first argument must be a Java object wrapper returned from an external Java function. The function returns true if the wrapped Java object is null. |
| intersection(node-set-1, node-set-2) | This returns a node-set that is the intersection of the two supplied node-sets, that is, it contains all the nodes that are in both sets. Note that the union operation can be done using the built-in operator "|". The intersection() function is deprecated: use the EXSLT intersection() function instead, for portability. |
| leading(node-set-1, stored-expression) | This returns a node-set containing all those nodes from node-set-1 up to and excluding the first one (in document order) for which the stored-expression evaluates to false. A stored expression may be obtained as the result of calling the saxon:expression() function. The stored expression is evaluated for each node in node-set-1 in turn, with that node as the context node, with the context position equal to the position of that node in node-set-1 (taken in document order), and with the context size equal to the size of node-set-1. Example: saxon:leading(following-sibling::*, saxon:expression('self::para')) will return the <para> elements following the current node, stopping at the first element that is not a </;para> Note: this function is quite different from the EXSLT leading() function, though both fulfil a similar purpose. |
| line-number() | This returns the line number of the context node in the source document within the entity that contains it. There are no arguments. If line numbers are not maintained for the current document, the function returns -1. (To ensure that line numbers are maintained, use the -l option on the command line) |
| lowest(node-set-1 [, stored-expression]) | This returns (as a node-set) the node from node-set-1 that has the lowest value of the supplied stored expression, evaluated as a number. If the stored expression is omitted, the expression "number(.)" is evaluated: that is, the string value of the node, converted to a number. A stored expression may be obtained as the result of calling the saxon:expression() function. The stored expression is evaluated for each node in node-set-1 in turn, with that node as the context node, with the context position equal to the position of that node in node-set-1, and with the context size equal to the size of node-set-1. Any NaN values are ignored. If the node-set is empty, the result is an empty node-set. If several nodes have the lowest value, the result node-set contains the one that is first in document order. This differs from the EXSLT lowest() function, which returns all the nodes that have the maximum value. Example: saxon:lowest(sale, saxon:expression('@price * @qty')) will evaluate price times quantity for each child <sale> element, and return the node for which this has the lowest value. |
| max(node-set-1 [, stored-expression]) | This returns the maximimum value of a numeric expression resulting from evaluating the supplied stored expression for each node in node-set-1 in turn, as a number. If the stored expression is omitted, the expression "number(.)" is evaluated: that is, the string value of the node, converted to a number. A stored expression may be obtained as the result of calling the saxon:expression() function. The stored expression is evaluated for each node in node-set-1 in turn, with that node as the context node, with the context position equal to the position of that node in node-set-1, and with the context size equal to the size of node-set-1. Any NaN values are ignored. If the node-set is empty, the result is negative infinity. For the single-argument version of this function, use the EXSLT max() function instead, for portability. Example: saxon:max(sale, saxon:expression('@price * @qty')) will evaluate price times quantity for each child <sale> element, and return the maximum amount. |
| min(node-set-1 [, stored-expression]) | This returns the minimum value of a numeric expression resulting from evaluating the supplied stored expression for each node in node-set-1 in turn, as a number. If the stored expression is omitted, the expression "number(.)" is evaluated: that is, the string value of the node, converted to a number. A stored expression may be obtained as the result of calling the saxon:expression() function. The stored expression is evaluated for each node in node-set-1 in turn, with that node as the context node, with the context position equal to the position of that node in node-set-1, and with the context size equal to the size of node-set-1. Any NaN values are ignored. If the node-set is empty, the result is positive infinity. For the single-argument version of this function, use the EXSLT min() function instead, for portability. Example: saxon:min(sale, saxon:expression('@price * @qty')) will evaluate price times quantity for each child <sale> element, and return the minimum amount. |
| node-set($fragment) | When version="1.1", a result-tree-fragment is converted implicitly
to a node-set if it is used in a context where a node-set is required. However, for
portability with other XSLT 1.0 processors, it may be better to use the EXSLT node-set() function.
The function takes a single argument that is a result tree fragment.
Its function is to convert the result tree fragment to a node-set. The resulting node-set contains a single
node, which is a root node (class DocumentInfo); below this are the actual nodes added to the result tree
fragment, which may be element nodes, text nodes, or anything
else. Note that a result tree fragment is not in general a well-formed document, for example there may
be multiple element nodes or text nodes as children of the root. |
| path() | This takes no arguments. It returns a string whose value is an XPath expression identifying the context node in the source tree. This can be useful for diagnostics, or to create an XPointer value, or when generating another stylesheet to process the same document. The resulting string can be used as input to the evaluate() function, provided that any namespace prefixes it uses are declared. |
| range(number-1, number-2) | The two arguments are converted to numbers and then rounded to integers. A new node-set is constructed containing one node for each integer in the range number-1 to number-2 inclusive; if number-2 is less than number-1 the result will be empty. The string-value of each node will be the relevant number; for example range(2, 5) generates a set of four nodes with string-values "2", "3", "4", and "5". The main intended usage is <xsl:for-each select="range($from, $to)"> which simulates a conventional for loop in other programming languages. |
| set-user-data(string, value) | This function sets user data associated with the context node in the source document. The data may be retrieved later (during the same stylesheet execution only) using the saxon:get-user-data() function. The string serves as a name for this property, allowing multiple pieces of user data to be associated with the same node. The value may be any XPath value. This function returns an empty string as its nominal result. Note: set-user-data() is particularly useful to save data read during preview mode processing (see saxon:preview) for later use during normal processing. However, take care (a) not to store the data with a node that will be deleted after the preview, and (b) not to store a node-set containing nodes that will be deleted after the preview. It is safest to store simple values such as strings and numbers: use the string() or number() function if necessary to do the conversion. Like saxon:assign, this function breaks the XSLT no-side-effects rule. There is always a risk that the Saxon optimizer will execute expressions more than once, or not at all, or in a different order from that expected. |
| sum(node-set-1, stored-expression) | This returns the total resuling from evaluating the supplied stored expression for each node in node-set-1 in turn, as a number. If the result is NaN for any node, the total will be NaN. A stored expression may be obtained as the result of calling the saxon:expression() function. The stored expression is evaluated for each node in node-set-1 in turn, with that node as the context node, with the context position equal to the position of that node in node-set-1, and with the context size equal to the size of node-set-1. Example: saxon:sum(sale, saxon:expression('@price * @qty')) will evaluate price times quantity for each child <sale> element, and return the total amount. |
| systemId() | This returns the system identifier (URI) of the entity in the source document that contains the context node . There are no arguments. |
| tokenize(string-1, string-2?) | The first argument is converted to a string and is treated as a list of separated tokens.
If the second argument is present, any character in string-2 is taken as a delimiter character,
and any sequence of delimiter characters is taken as a token separator. If the second argument
is omitted, any sequence of whitespace is taken as a token separator: or to put it another way,
the default for string-2 is '	

 '. A new node-set is constructed containing one node for each token; if the string is empty or contains a separator only then the result will be empty. The string-value of each node will be the relevant token; for example tokenize("a cup of tea") generates a set of four nodes with string-values "a", "cup", "of", and "tea". |
The source code of these methods, which in most cases is extremely simple, can be used as an example for writing other user extension functions. It is found in class com.icl.saxon.functions.Extensions
A SAXON extension element is invoked using a name such as <saxon:localname>.
The saxon prefix (or whatever prefix you choose to use) must be associated with the SAXON namespace URI "http://icl.com/saxon". The prefix must also be designated as an extension element prefix by including it in the extension-element-prefixes attribute on the xsl:stylesheet element, or the xsl:extension-element-prefixes attribute on any enclosing literal result element or extension element.
However, top-level elements such as saxon:handler and saxon:preview can be used without designating the prefix as an extension element prefix.
The saxon:assign element is used to change the value of a local or global variable that has previously been declared using xsl:variable (or xsl:param). The variable or parameter must be marked as assignable by including the extra attribute saxon:assignable="yes"
As with xsl:variable, the name of the variable is given in the mandatory name attribute, and the new value may be given either by an expression in the select attribute, or by expanding the content of the saxon:assign element
Example:
<xsl:variable name="i" select="0" saxon:assignable="yes"/>
<saxon:while test="$i < 10">
The value of i is <xsl:value-of select="$i"/>
<saxon:assign name="i" select="$i+1"/>
</saxon:while>
|
The saxon:doctype instruction is used to insert a document type declaration into the current output file. It must be instantiated before the first element in the output file is written.
The saxon:doctype instruction takes no attributes. The content of the element is a template-body that is instantiated to create an XML document that represents the DTD to be generated; this XML document is then serialized using a special output method that produces DTD syntax rather than XML syntax.
If this element is present the doctype-system and doctype-public attributes of xsl:output are ignored
The generated XML document uses the following elements, where the namespace prefix "dtd" is used for the namespace URI "http://icl.com/saxon/dtd":
| dtd:doctype | Represents the document type declaration. This is always the top-level element. The element
may contain dtd:element, dtd:attlist, dtd:entity, and dtd:notation elements. It may have the following
attributes: name (mandatory) The name of the document type system The system ID public The public ID |
| dtd:element | Represents an element type declaration. This is always a child of dtd:doctype. The element
is always empty. It may have the following attributes: name (mandatory) The name of the element type content (mandatory) The content model, exactly as it appears in a DTD, for example content="(#PCDATA)" or content="( a | b | c)*" |
| dtd:attlist | Represents an attribute list declaration. This is always a child of dtd:doctype. The element
will generally have one or more dtd:attribute children. It may have the following attributes: element (mandatory) The name of the element type |
| dtd:attribute | Represents an attribute declaration within an attribute list.
This is always a child of dtd:attlist. The element
will always be empty. It may have the following attributes: name (mandatory) The name of the attribute type (mandatory) The type of the attribute, exactly as it appears in a DTD, for example type="ID" or type="( red | green | blue)" value (mandatory) The default value of the attribute, exactly as it appears in a DTD, for example value="#REQUIRED" or value="#FIXED 'blue'" |
| dtd:entity | Represents an entity declaration.
This is always a child of dtd:doctype. The element may be empty, or it may have content. The
content is a template body, which is instantiated to define the value of an internal parsed
entity. Note that this value includes the delimiting quotes. The xsl:entity element
may have the following attributes: name (mandatory) The name of the entity system The system identifier public The public identifier parameter Set to "yes" for a parameter entity notation The name of a notation, for an unparsed entity |
| dtd:notation | Represents a notation declaration.
This is always a child of dtd:doctype. The element will always be empty. It
may have the following attributes: name (mandatory) The name of the notation system The system identifier public The public identifier |
Note that Saxon will perform only minimal validation on the DTD being generated; it will output the components requested but will not check that this generates well-formed XML, let alone that the output document instance is valid according to this DTD.
Example:
<xsl:template match="/">
<saxon:doctype xsl:extension-element-prefixes="saxon">
<dtd:doctype name="booklist"
xmlns:dtd="http://icl.com/saxon/dtd" xsl:exclude-result-prefixes="dtd">
<dtd:element name="booklist" content="(book)*"/>
<dtd:element name="book" content="EMPTY"/>
<dtd:attlist element="book">
<dtd:attribute name="isbn" type="ID" value="#REQUIRED"/>
<dtd:attribute name="title" type="CDATA" value="#IMPLIED"/>
</dtd:attlist>
<dtd:entity name="blurb">'A <i>cool</i> book with > 200 pictures!'</dtd:entity>
<dtd:entity name="cover" system="cover.gif" notation="GIF"/>
<dtd:notation name="GIF" system="http://gif.org/"/>
</dtd:doctype>
</saxon:doctype>
<xsl:apply-templates/>
</xsl:template> |
Although not shown in this example, there is nothing to stop the DTD being generated as the output of a transformation, using instructions such as xsl:value-of and xsl:call-template. It is also possible to use xsl:text with disable-output-escaping="yes" to output DTD constructs not covered by this syntax, for example conditional sections and references to parameter entities.
The saxon:entity-ref element is useful to generate entities such as in HTML output. To do this, write:
<saxon:entity-ref name="nbsp"/>
|
The saxon:function element is used to declare an extension function implemented in the XSLT language. The effect is identical to the func:function element defined in EXSLT, and the EXSLT version should be used in preference, for portability.
This is a top-level element; its content is a template-body, optionally preceded by one or more xsl:param elements.
There must be a name attribute; its value is a QName, and it must have a non-null namespace URI.
The function definition will normally contain one or more saxon:return instructions to define the return value; if the function exits without encountering a saxon:return, the result is an empty string. It is an error if more than one saxon:return instruction is instantiated (remember that the execution model is not sequential, so saxon:return does not cause an immediate exit - it merely defines the return value.).
The parameters are interpreted positionally. If there are more parameters declared using xsl:param than are supplied in the function call, the excess parameters take their default values. It is an error to have more arguments in the function call than there are parameters declared in the function body.
In a function call where the function name has a non-null namespace URI, the system searches first for a matching saxon:function definition, then for an external Java function. If there are several functions with the same name, the one with highest import precedence is chosen; if there are several of these, the one that appears last in the stylesheet wins.
Calling a function does not change the current node or the values of position() and last().
A function body may contain local variables in the same way as a template body.
Functions provide an alternative to named templates. The main differences are that the syntax for calling them is simpler (it is a standard XPath function call) and that they can return a value of any type.
A function is not allowed to write anything to the result tree. More precisely, it is not allowed to write to the current output destination of the code that calls it. It is, however, allowed to create a new result tree fragment within the code of the function, or a new xsl:document destination, and write to this. The reason for this restriction is that it is generally unpredictable when and how often a function will be called, especially if it is used inside a predicate, so it is safest for it to have no side-effects.
One particular use for XSLT extension functions is to provide wrappers for Java extension functions, making them more convenient to call from XPath expressions. Another use is in contexts where named templates cannot be called, for example in the expressions used to define a named key (xsl:key) or a sort key (xsl:sort), or in the predicate of a match pattern.
The saxon:function element automatically declares the Saxon namespace as an extension namespace, so that saxon:return is recognized.
Example:
<saxon:function name="my:initial">
<xsl:param name="size"/>
<saxon:return select="substring(.,1,$size)"/>
</saxon:function>
<xsl:template match="text()">
<xsl:value-of select="my:initial(3)"/>
</xsl:template>
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The <saxon:group> element causes iteration over the nodes selected by a node-set expression.
There is a mandatory attribute, select, which defines the nodes over which the statement will iterate. This is analogous to the select attribute of <xsl:for-each>
There is also a mandatory group-by attribute to control grouping. The value of this attribute is a string expression, which is applied to each item selected by the select expression. The XSL statements subordinate to the <saxon:group> element are applied once to each group of consecutive source nodes selected by the select expression that have the same value for the group-by expression.
The <saxon:group> element may have one or more <xsl:sort> child elements to define the order of sorting. The sort keys are specified in major-to-minor order. Note that group-by does not itself cause sorting, but it can conveniently be used in conjunction with sorting. The group-by key will often be the same as the major sort key.
The <saxon:group> element must contain somewhere within it an <saxon:item> element. The XSL instructions outside the <saxon:item> element are executed only once for each group of consecutive elements with the same value for the grouping key; the instructions within the saxon:item are executed once for each individual item in the saxon:group selection.
The context for the select expression is the usual context for expressions within an XSL element, i.e. it is based on the current node and current node list of the containing template body.
The context for the group-by expression is as if the expression were written inside the saxon:group loop. If the select expression selects a node-set S, then for each node N within S, the group-by expression is evaluated with N as the context node, with count(S) as the context size, and with the context position taking the values 1..count(S) in turn. The context position represents the position of the node in the node-set after sorting.
If there is an <xsl:sort> element present, then the context for evaluating the sort key follows exactly the same rules as for <xsl:for-each>. In particular, the context position is the position before sorting.
Within the <saxon:group> element, and also within the <saxon:item>; element, the context reflects the full node-set being processed (that is, the node-set selected by the select attribute). The context position is the position of the node within this node-set, and the context size is the size of this node-set. It is not possible to determine the size of an individual group, or the position of the current node within an individual group. The instructions preceding <saxon:item> are executed with the first node of a group as the current node, and the instructions following <saxon:item> are executed with the last node of a group as the current node.
The expressions used for sorting and grouping can be any string expressions. The following are particularly useful:
Example: This example groups the BOOK elements having the same AUTHOR.
The saxon:handler element is used at the top level of the stylesheet, in the same way as xsl:template. It takes attributes match, mode, name, and priority in the same way as xsl:template, and is considered along with all XSL templates when searching for a template to execute in response to xsl:apply-templates or xsl:call-template. However, the action performed when a saxon:handler is invoked is to call the user-written Java NodeHandler named in the mandatory handler attribute.
The Java node handler must be written as a subclass of com.icl.saxon.handlers.NodeHandler. It is supplied with a Context parameter, which gives access to a wide range of information and services, including the current context in the source document, any parameters on the call, and the Outputter object used to write to the result tree. The Context parameter also provides access to a method applyTemplates() which allows the Java node handler to make a call back to process XSLT templates in the stylesheet.
The saxon:item element is always used within a saxon:group element. The XSL instructions outside the saxon:item element are executed once for each group (that is, each group of consecutive items with the same value for the group-by expression), while the XSL instructions within the saxon:item element are executed once for each individual item.
See saxon:group for further details.
The saxon:output instruction is a synonym for
xsl:document, introduced
in the working draft of XSLT 1.1. While xsl:document is available only when
version="1.1", saxon:output is always available, provided the
relevant namespace is declared as an extension namespace.
The attributes are identical to those of xsl:document.
The saxon:preview element is a top-level element used to identify elements in the source document that will be processed in preview mode. The purpose of preview mode is to enable XSLT processing of very large documents that are too big to fit in memory: the idea is that subtrees of the document can be processed and then discarded as soon as they are encountered.
There are two mandatory attributes: mode identifies the mode in which the relevant templates will be applied, and elements is a space-separated list of element names that will be processed in preview mode.
While the source XML document is being read, if an element end tag is encountered for an element that is in the list of preview elements, the relevant template is found (using the normal matching rules, with mode equal to the specified preview mode). This template is then executed. After the template has completed execution, the child nodes of the preview element (but not the element itself, nor its attributes) are deleted from the tree to save memory.
During the matching of a preview element and during the execution of the preview template, only part of the source document is visible. This part includes the ancestors of the preview element, the descendants of the preview element, and all nodes that precede the preview element in document order, except for nodes that are descendants of another preview element.
Global variables are not available to a preview template. The supplied values of global parameters are available, but not the default values of unsupplied parameters.
A preview template may write to a secondary output destination using saxon:output, or it may set global variables using saxon:assign. It can save information using the extension function setUserData(), which can be accessed later using getUserData(). This is useful to save information that would otherwise disappear when the subtree rooted at the preview element is deleted from the tree. The preview template may also write directly to the principal output destination, but note that in this case each instantiation of the preview template will produce a subtree immediately below the root of the output tree. Normally this means the output document will have multiple element nodes as children of the root. This is not well-formed XML, but you can easily construct a well-formed XML document by referencing this file as an external entity.
One simple use for saxon:preview is simply to delete unwanted parts of the tree to reduce the amount of memory needed. In this case, just provide a preview template that does nothing.
Preview templates are called while the tree is being built. When the tree has been completely built, it will contain the preview elements themselves, but any nodes that were descendants of the preview elements will have been deleted. At this stage the stylesheet is applied to the root of the tree, in "default" mode, in the normal way. If you don't want any further processing to take place at this stage, write a root template that does nothing: <xsl:template match="/"/>.
<saxon:preview> is not supported when a transformation is run using the JAXP 1.1 TransformerHandler interface. It works when using the Saxon command line, or when invoking a transformation using the transform() method.
The saxon:return element is an instruction that can only occur within a saxon:function definition. It must not have any following sibling instructions other than xsl:fallback. However, there can be more than one saxon:return instruction in a function, for example one in each branch of an xsl:choose. The saxon:return instruction is a synonym of the EXSLT func:result instruction: the EXSLT version is preferred, for portability reasons.
Instantiating a saxon:return element causes exit from the call of the enclosing saxon:function.
The saxon:return element has an optional select attribute, whose value is an XPath expression. If the select attribute is present, this expression is evaluated and its value constitutes the return value of the function. If it is absent, the content of the saxon:return element is instantiated and the result is returned as a result tree fragment. If the element is empty and has no select attribute, the function returns an empty string.
If a function completes without instantiating a saxon:return instruction, the return value of the function is an empty string. It is an error for a function to instantiate more than one saxon:return instruction.
The saxon:script element is a top-level element. It is a synonym of
xsl:script, except that it is available
regardless of the setting of the version attribute on xsl:stylesheet.
The reason for providing saxon:script as a separate element is that any processor other than Saxon will ignore it. This makes it possible to define an implementation for an extension function that will be used by Saxon, but not by other processors. With other processors, a different implementation can be selected, using mechanisms defined by that processor (for example, xalan:script).
If you want to use extension functions such as xx:intersection() which are available as built-in extensions in several XSLT processors, you can define the Saxon implementation as follows:
The saxon:while element is used to iterate while some condition is true.
The condition is given as a boolean expression in the mandatory test attribute. Because this expression must change its value if the loop is to terminate, the condition will always reference a variable that is updated somewhere in the loop using an saxon:assign element.
Example:
<xsl:variable name="i" expr="0"/>
<saxon:while test="$i < 10">
The value of i is <xsl:value-of select="$i"/>
<saxon:assign name="i" expr="$i+1"/>
</saxon:while>
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Michael H. Kay
14 November 2001