XSLT 2.0 and XPath 2.0 Programmer's Reference, 4th Edition (512 page)

• The KindTest
  element(QName, QName)
  tests both the name of the node and its type: the name must match the first
  QName
  , or the name of one of the elements in its substitution group, and the type annotation must match the second
  QName
  (which must be the name of a top-level type definition in an imported schema). Again, if the element includes the attribute
  xsi:nil = “true”
  , then it will match this
  KindTest
  only if the second
  QName
  is followed by the symbol
  ?
  .
  

KindTests for Attribute Nodes

KindTests
for attribute nodes follow the same format as those for element nodes, with minor variations. The same options are available, though in practice they are likely to be used rather differently. In particular, global attribute declarations are not used very often in XML Schema, and matching against the names of a top-level simple type definition is probably a more likely scenario.

• attribute(QName)
  matches any attribute whose name matches the given
  QName
  : as a pattern, this means exactly the same as
  @QName
  or
  attribute::QName
  .
  
• schema-attribute(QName)
  is used to test for an attribute that matches a top-level attribute declaration in the schema identified by the given
  QName
  . It's an error to use this form unless you have imported a schema containing this top-level attribute declaration. The attribute is considered to match if two conditions are satisfied:
  
  • Its name is the same as the QName.
    
  • The type of the attribute node, identified from its type annotation, matches the type defined for this attribute declaration in the schema.
    
• attribute(*, QName)
  is used to test for an attribute whose type annotation indicates that it has been successfully validated against the schema-defined simple type definition identified by the
  QName
  . The
  QName
  can identify a built-in type such as
  xs:dateTime
  , or a type (it will always be a simple type) that is the subject of a named type definition in an imported schema. The test will match any attribute that has a type annotation that refers to the named type, or a type derived from the named type by restriction. For example, the
  KindTest
  attribute(*, xs:date)
  matches any attribute whose type (as established by schema validation) is
  xs:date
  .
  
• The
  KindTest
  attribute(QName, QName)
  is essentially a combination of
  attribute(QName)
  and
  attribute(*, QName)
  . This tests both the name of the node and its type: the name must match the first QName, and the type annotation must match the second QName (which must be the name of a top-level simple type definition in an imported schema).