## com.saxonica.schema
Class UnionSelection

    java.lang.Object
      com.saxonica.schema.UnionSelection

All Implemented Interfaces:
  Selection

    public class UnionSelection

extends java.lang.Object
implements Selection

A union selection is a selection consisting of several alternatives separated by "|"

Field Summary

Fields inherited from interface com.saxonica.schema.Selection
`MATCHES_AS_PARENT, MATCHES_AS_SELF`

Constructor Summary
`UnionSelection(Selection p1, Selection p2)` Create a union selection

Method Summary
`boolean` `canMatchAttributes()` Determine whether the selection can match attribute nodes
`boolean` `canMatchElementContent()` Determine whether the selection can match element content
`void` `displayExpression(ExpressionPresenter out)` Diagnostic print of expression structure.
`ItemType` `getItemType(TypeHierarchy th)` Return the type of the nodes selected by this selection
`boolean` `matchesAttribute(int fingerprint)` Determine whether a given attribute matches the Selection
`int` `matchesElement(int[] stack, int length, int contextPosition)` Determine whether the selector matches a given element.
`java.lang.String` `typeCheck(ExpressionVisitor visitor, ItemType contextItemType)` Check that the selection makes sense in the context of a given ItemType.

Methods inherited from class java.lang.Object
`clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait`

Constructor Detail

### UnionSelection

    public UnionSelection(Selection p1,
                          Selection p2)

  Create a union selection

  Parameters:
    `p1` - the first alternative
    `p2` - the second alternative

Method Detail

### matchesElement

    public int matchesElement(int[] stack,
                              int length,
                              int contextPosition)

  Determine whether the selector matches a given element. The element is identified by an array of integers representing the fingerprints of the names of this element and each of its ancestors, in document order (i.e., root element first, matched element last).

  Specified by:
    `matchesElement` in interface `Selection`
  Parameters:
    `stack` - the array of name fingerprints
    `length` - the effective length of the array; any items beyond this position are ignored
    `contextPosition` - the position in this array of the context element for the selection.
  Returns:
    a bit-significant integer. {#MATCHES_AS_SELF} is set if the element matches the selector in its own right. {#MATCHES_AS_PARENT} is set if the element is a potential parent of an attribute that matches the selector. In the case of a union selection, it is possible for both bits to be set.

### matchesAttribute

    public boolean matchesAttribute(int fingerprint)
                             throws ValidationException

  Determine whether a given attribute matches the Selection

  Specified by:
    `matchesAttribute` in interface `Selection`
  Parameters:
    `fingerprint` - the integer nameCode of an attribute
  Returns:
    true if it matches, false if it does not match
  Throws:
    `ValidationException` - if there is more than one attribute that matches

### canMatchAttributes

    public boolean canMatchAttributes()

  Determine whether the selection can match attribute nodes

  Specified by:
    `canMatchAttributes` in interface `Selection`
  Returns:
    true if the selection can match attributes

### canMatchElementContent

    public boolean canMatchElementContent()

  Determine whether the selection can match element content

  Specified by:
    `canMatchElementContent` in interface `Selection`
  Returns:
    true if the selection can match elements

### typeCheck

    public java.lang.String typeCheck(ExpressionVisitor visitor,
                                      ItemType contextItemType)

  Check that the selection makes sense in the context of a given ItemType. Return null if the selection is OK, otherwise an error message

  Specified by:
    `typeCheck` in interface `Selection`
  Parameters:
    `visitor` - the expression visitor
    `contextItemType` - the type of the context item
  Returns:
    an error messge if the expression is invalid

### getItemType

    public ItemType getItemType(TypeHierarchy th)

  Return the type of the nodes selected by this selection

  Specified by:
    `getItemType` in interface `Selection`
  Parameters:
    `th` - the type hierarchy cache
  Returns:
    the item type of the selected nodes

### displayExpression

    public void displayExpression(ExpressionPresenter out)

  Diagnostic print of expression structure. The abstract expression tree is written to the supplied output destination.

  Specified by:
    `displayExpression` in interface `Selection`
  Parameters:
    `out` - the place where the structure is to be written

Copyright (c) Saxonica Limited. All rights reserved.