in XSLT, How to find the namespace of an XML element attribute?

Trying to use the function namespace-uri to find the namespace of an attribute.

<xsl:template match="xse:seeAlso">
<xsd:xmlEntityReference xml:space="preserve">
    <xsl:value-of select="namespace-uri()"/>#E/<xsl:value-of select="@ref"/>
</xsd:xmlEntityReference>
</xsl:template>

I want the namespace for the "ref" attribute of the element. Any tip?

UPDATE 1 To make it clearer, I want the namespace of the element referenced by the "ref" attribute. Sorry for any confusion.

UPDATE 2 @empo: This is snippet of one of the schemas

<?xml version="1.0" encoding="utf-8"?>
<xs:schema xmlns:html="http开发者_运维知识库://www.w3.org/1999/xhtml"
            xmlns:wix="http://schemas.microsoft.com/wix/2006/wi"
             xmlns:xs="http://www.w3.org/2001/XMLSchema"
            xmlns:xse="http://schemas.microsoft.com/wix/2005/XmlSchemaExtension"
      targetNamespace="http://schemas.microsoft.com/wix/IIsExtension"
                xmlns="http://schemas.microsoft.com/wix/IIsExtension">

    <xs:import namespace="http://schemas.microsoft.com/wix/2006/wi" />

    <xs:element name="Certificate">
        <xs:annotation>
            <xs:documentation>
                Used to install and unintall certificates.
            </xs:documentation>
            <xs:appinfo>
                <xse:seeAlso ref="CertificateRef"/>
            </xs:appinfo>
        </xs:annotation>
        <xs:complexType>
            <!-- Cut off -->
        </xs:complexType>
    </xs:element>

    <xs:element name="CertificateRef">
        <xs:annotation>
            <xs:documentation>
                ...
            </xs:documentation>
            <xs:appinfo>
                <xse:seeAlso ref="Certificate"/>
            </xs:appinfo>
        </xs:annotation>
        <xs:complexType>
            <!-- Cut off -->
        </xs:complexType>
    </xs:element>
</xs:schema>

This is a sample of the transform

<?xml version="1.0" encoding="utf-8"?>
<xsl:stylesheet version="1.0"
                xmlns:xsl="http://www.w3.org/1999/XSL/Transform"
                xmlns:msxsl="urn:schemas-microsoft-com:xslt"
                xmlns:xsd="http://schemas.xsddoc.codeplex.com/schemaDoc/2009/3"
                xmlns:ddue="http://ddue.schemas.microsoft.com/authoring/2003/5"
                xmlns:xlink="http://www.w3.org/1999/xlink"
                xmlns:xs="http://www.w3.org/2001/XMLSchema"
                xmlns:xse="http://schemas.microsoft.com/wix/2005/XmlSchemaExtension"
                xmlns:xhtml="http://www.w3.org/1999/xhtml"
                exclude-result-prefixes="msxsl xs xse">
  <xsl:output method="xml" indent="yes"/>

  <xsl:param name="parentItemType"/>
  <xsl:param name="parentItemNamespace"/>
  <xsl:param name="parentItemUri"/>

  <xsl:param name="currentItemType"/>
  <xsl:param name="currentItemNamespace"/>
  <xsl:param name="currentItemUri"/>

  <xsl:template match="*">
    <xsl:apply-templates select="xs:annotation" />
  </xsl:template>

  <xsl:template match="xse:seeAlso">
    <xsd:xmlEntityReference xml:space="preserve">
        <xsl:value-of select="namespace-uri()"/>#E/<xsl:value-of select="@ref"/>
    </xsd:xmlEntityReference>
  </xsl:template>

</xsl:stylesheet>

If the value of the @ref attribute is selected as shown, then the namespace URI value would be nothing. The attribute would be in the "unnamed namespace" (or "null namespace") and it won't have a namespace URI value.

If an attribute is bound to a namespace, then it will have a namespace prefix and would need to be addressed as such in the XPath (e.g. @foo:ref).

You can verify this and obtain the namespace URI of the attribute(or any element or attribute node) passing it as a parameter to the namespace-uri() function.

namespace-uri(@ref)

To make it clearer, I want the namespace of the element referenced by the "ref" attribute. Sorry for any confusion

You are searching for following

 <xsl:value-of select="namespace-uri(//*[@name=current()/@ref])"/>

or, even:

 <xsl:value-of select="namespace-uri(//xs:element[@name=current()/@ref])"/>