I have a xsl:function which :
- must return a element()
- has a string param "foobar".

I typed $foobar as xs:string but I'd like to restrict the possible values to "foo" or "bar".
I know it's possible to define such a constrain in a xsd schema, but is there a way to do that in xpath2 ?

<xsl:import-schema>
<xs:schema targetNamespace="urn:local:foobar">
<xs:simpleType name="foobarType">
<xs:restriction base="xs:string">
<xs:enumeration value="foo"/>
<xs:enumeration value="bar"/>
</xs:restriction>
</xs:simpleType>
</xs:schema>
</xsl:import-schema>

<xsl:function name="igs:get-css-rule" as="element()">
<xsl:param name="foobar" as="fb:foobarType"/>
  ....

This typing is important because the returned element() is selected from a xsl:choose on $foobar value (with no otherwise) :

My code looks like :
<xsl:function name="igs:get-css-rule" as="element()">
<xsl:param name="foobar" as="xs:string"/> <!--(foo|bar)-->
<xsl:choose>
<xsl:when test="$foobar='foo'">
<xsl:sequence select="igs:get-my-foo-item()"/>
</xsl:when>
<xsl:when test="$css='bar'">
<xsl:sequence select="igs:get-my-bar-item()"/>
</xsl:when>
</xsl:choose>
</xsl:function>

And I get such a parsing error on my xslt :
XTTE0570: Conditional expression: If none of the conditions is satisfied, an empty
sequence will be returned, but this is not allowed [...]

Michael Kay
Saxonica