Named item types

A named item type is an item type identified by an expanded QName: namespace-uri, namespace-prefix and local name. These can be defined in XSLT or XQuery, and used wherever an item type may appear (for example in a function signature or variable declaration, or in instance of or cast as expressions).

Named item types are useful because they abstract away from the detail of how a type is implemented: for example cx:complex is more meaningful than record(r as xs:double, i as xs:double), and it creates more scope for changing the way types are represented as the software evolves.

Note that the syntax for referencing named item types has changed in Saxon 13, to align with changes in the 4.0 specifications. The syntax type(T) is dropped. A named item type T is now referenced simply as T, not type(T). In XSLT patterns, a match for items of type T is written match="~T" rather than match="type(T)".

In XSLT, named item types can be defined using the top-level declaration xsl:item-type. For example:

<xsl:item-type name="cx:complex" as="record(r as xs:double, i as xs:double)"/> <xsl:function name="cx:complex" as="cx:complex"> <xsl:param name="r" as="xs:double"/> <xsl:param name="i" as="xs:double"/> <xsl:sequence select="map{'r':$r, 'i':$i}"/> </xsl:function> <xsl:function name="cx:add" as="cx:complex"> <xsl:param name="x" as="cx:complex"/> <xsl:param name="y" as="cx:complex"/> <xsl:sequence select="cx:complex($x?r + $y?r, $x?i + $y?i)"/> </xsl:function>

XSLT-defined named item types are scoped to a package. The usual rules for import precedence apply.

If you want to use the same named item types in multiple packages, define them in a module of their own, and include that module in each package using xsl:include.

Named item types can be used in XSLT 4.0 match patterns, for example:

<xsl:template match="~cx:complex[?i=0]">{?r}</xsl:template> <xsl:template match="~cx:complex">{?r}{if (?i ge 0) then '+' else ''}{?i}i</xsl:template>

In XQuery, named item types can be declared in the query prolog. For example:

declare type cx:complex as record(r as xs:double, i as xs:double);