XSLT 2.0 and XPath 2.0 Programmer's Reference, 4th Edition (184 page)

Usage

It's not necessary to import every schema that has been used to validate an input document. You only need to import the schema if there is code in the stylesheet that actually references the names whose meaning is defined in the schema.

The places where such references may occur are as follows:

• In the
  type
  attribute of
  
  ,
  
  ,
  
  ,
  
  ,
  
  ,
  
  , and the
  xsl:type
  attribute of literal result elements. This is always a
  QName
  identifying a top-level type definition, and unless it is one of the built-in types such as
  xs:integer
  , the schema in which the type is defined must be imported.
  
• In the
  as
  attribute of
  
  ,
  
  ,
  
  ,
  
  , and
  
  . The value of this attribute is a description of an XPath type and is expressed using the
  SequenceType
  syntax defined in Chapter 11. If the
  SequenceType
  references the name of an atomic type, this will be a
  QName
  identifying either a built-in type such as
  xs:date
  , or a top-level simple type definition in a schema. If the latter is the case, the schema must be imported. If the
  SequenceType
  uses the constructs
  element(N, T)
  or
  attribute(N, T)
  then the rules are slightly more complicated, and are described below.
  
• In an XPath expression anywhere in the stylesheet that uses a
  SequenceType
  . This construct is used in expressions such as
  $x instance of T
  or
  $x treat as T
  . The rules here are the same as for a
  SequenceType
  appearing in an
  as
  attribute, as described in the previous item.
  
• In an XPath expression that uses a constructor function for a user-defined atomic type (for example
  mf:part-number(‘PXW5792’)
  ) or a cast to a user-defined atomic type (for example
  ’PXW5792’ cast as mf:part-number
  ). In both these cases, the type name must be the name of a top-level simple type definition, and the schema containing this type definition must be imported.