xsl:param

Used to define a formal parameter to a template, the stylesheet, a function, or an iteration.

Category: declaration
Content: sequence-constructor
Permitted parent elements: xsl:package ; xsl:stylesheet ; xsl:transform ; xsl:override ; xsl:function ; xsl:template ; xsl:iterate

Attributes

name

eqname

The name of the parameter.

select?

expression

The default value of the parameter may be defined either by a select attribute, or by the contents of the xsl:param element, in the same way as for xsl:variable. The default value is ignored if an actual parameter is supplied with the same name.

as?

sequence-type

Defines the required type of the parameter. The supplied value of the parameter will be converted to this type if required. If the parameter is omitted, the default value must conform to the type. Note that if no default is specified, the default is a zero-length string, which may conflict with the required type.

required?

boolean

Not allowed for function parameters, which are always required. If the parameter is required, no default value may be specified. Failure to supply a value for a required parameter gives a run-time error (the specification says that in the case of xsl:call-template, it should be a static error).

tunnel?

boolean

The value yes may be specified only for template parameters, and indicates that the parameter is a tunnel parameter. Tunnel parameters are automatically passed on by the called template to any further templates that it calls, and so on recursively. The default is no.

static?

boolean

The value yes may be specified only for stylesheet parameters, and indicates that the parameter is a static parameter (that is, its value is known during static analysis of the stylesheet). The default is no.

saxon:as?

Allows additional type information to be supplied using Saxon extension syntax. For details see saxon:as.

saxon:assignable?

boolean

May be set on global variables. Setting the value to yes ensures that the variable is actually evaluated, which is useful if the select expression calls extension functions with side-effects; without this, a variable that is never referenced may never be evaluated. For details see saxon:assignable.

Notes on the Saxon implementation

It is strongly recommended to use the as attribute to declare the expected type of a parameter. Not only does this help debugging (by catching errors closer to the point where they occur), it also helps the Saxon optimizer generate more efficient code.

XSLT 3.0 introduces static parameters (global parameters declared with static="yes"). These are implemented since Saxon 9.5. The value of a static parameter must be known at stylesheet compile time. Static parameters can be referenced in [xsl:]use-when attributes, and also in the initializers of other static parameters and variables. The scope rules are a little different from other global variables and parameters - forwards references are not allowed. The values of static parameters may be supplied from the command line in the same way as dynamic parameters; they may also be supplied via a new method call on the s9api XsltCompiler object.

In standard XSLT, the value of a global variable cannot be updated once it has been declared using xsl:param. Saxon however provides a saxon:assign extension element to circumvent this restriction. The extension attribute saxon:assignable must be set to yes on the relevant xsl:param in order to use this feature.

The type-information attribute was removed at Saxon 7.5.

Details

As a template parameter, xsl:param must be used as an immediate child of the xsl:template element. As a stylesheet parameter, it must be used as an immediate child of the xsl:stylesheet element.

In XSLT 2.0, xsl:param can appear as a child of xsl:function, as a function parameter.

In XSLT 3.0, xsl:param can also appear as a child of xsl:iterate, as an iteration parameter.

Links to W3C specifications

XSLT 2.0 Specification

XSLT 3.0 Specification

See also

xsl:apply-templates

xsl:call-template

xsl:iterate

xsl:variable

xsl:with-param