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`	In XSLT 3.0 and earlier, this attribute is not allowed for function parameters, which are always required; but in XSLT 4.0 function parameters can be optional. 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?`	`sequence-type`	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.

Saxon availability

Available in XSLT 1.0 and later versions. Available in all Saxon editions. Available for all platforms.

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.

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.

In XSLT 4.0, function parameters can be optional, with a default value supplied.

Links to W3C specifications

XSLT 3.0 Specification

XSLT 4.0 Specification