xsl:QName 

A QName.
This schema does not use the built-in type xs:QName, but rather defines its own
QName type. Although xs:QName would define the correct validation on these attributes,
a schema processor would expand unprefixed QNames incorrectly when constructing the PSVI,
because (as defined in XML Schema errata) an unprefixed xs:QName is assumed to be in
the default namespace, which is not the correct assumption for XSLT.
The data type is defined as a restriction of the built-in type Name, restricted
so that it can only contain one colon which must not be the first or last character.

Simple Type Information

Used By

Attributes xsl:attribute-set/@name, xsl:attribute/@type, xsl:call-template/@name, xsl:character-map/@name, xsl:copy-of/@type, xsl:copy/@type, xsl:decimal-format/@name, xsl:document/@type, xsl:element/@type, xsl:function/@name, xsl:key/@name, xsl:literal-result-element-attributes/@xsl:type, xsl:output/@name, xsl:param/@name, xsl:result-document/@type, xsl:sequence-constructor-group/@name, xsl:sequence-constructor-group/@type, xsl:template/@name, xsl:variable/@name, xsl:with-param/@name

Source 

<xs:simpleType name="QName">
  <xs:annotation>
    <xs:documentation>A QName. This schema does not use the built-in type xs:QName, but rather defines its own QName type. Although xs:QName would define the correct validation on these attributes, a schema processor would expand unprefixed QNames incorrectly when constructing the PSVI, because (as defined in XML Schema errata) an unprefixed xs:QName is assumed to be in the default namespace, which is not the correct assumption for XSLT. The data type is defined as a restriction of the built-in type Name, restricted so that it can only contain one colon which must not be the first or last character.</xs:documentation>
  </xs:annotation>
  <xs:restriction base="xs:Name">
    <xs:pattern value="([^:]+:)?[^:]+"/>
  </xs:restriction>
</xs:simpleType>