Table of contents

Appendices

2.3 Node Tests

Every axis has a principal node type. If an axis can contain elements, then the principal node type is element; otherwise, it is the type of the nodes that the axis can contain. Thus,

For the attribute axis, the principal node type is attribute.

For the namespace axis, the principal node type is namespace.

For other axes, the principal node type is element.

A node test that is a QName is true if and only if the type of the node (see Data Model) is the principal node type and has an [expanded-name] equal to the [expanded-name] specified by the QName. For example, child::para selects the para element children of the context node; if the context node has no para children, it will select an empty set of nodes. attribute::href selects the href attribute of the context node; if the context node has no href attribute, it will select an empty set of nodes.

A QName in the node test is expanded into an [expanded-name] using the namespace declarations from the expression context. This is the same way expansion is done for element type names in start and end-tags except that the default namespace declared with xmlns is not used: if the QName does not have a prefix, then the namespace URI is null (this is the same way attribute names are expanded). It is an error if the QName has a prefix for which there is no namespace declaration in the expression context.

A node test * is true for any node of the principal node type. For example, child::* will select all element children of the context node, and attribute::* will select all attributes of the context node.

A node test can have the form NCName:*. In this case, the prefix is expanded in the same way as with a QName, using the context namespace declarations. It is an error if there is no namespace declaration for the prefix in the expression context. The node test will be true for any node of the principal type whose [expanded-name] has the namespace URI to which the prefix expands, regardless of the local part of the name.

The node test text() is true for any text node. For example, child::text() will select the text node children of the context node. Similarly, the node test comment() is true for any comment node, and the node test processing-instruction() is true for any processing instruction. The processing-instruction() test may have an argument that is [Literal] ; in this case, it is true for any processing instruction that has a name equal to the value of the [Literal] .

A node test node() is true for any node of any type whatsoever.