IE5 Conformance
IE5 implements a subset of XPath. If you are developing for the MSXML objects
in the initial IE5 release, you have to know what features are implemented in
XPath and which are not. Microsoft has committed to implementing the full standard
in all later versions. It is unclear what backward compatibility will exist
with syntax elements that are not part of the W3C recommendation. Here we will
show the differences between the IE5 implementation and the W3C recommendation
1.0.
Axes
IE5 knows only the abbreviated syntax for axis and node test. You cannot use
the syntax with a double colon. This limits the number of axes, because not
all XPath axes have an abbreviated form (for example namespace,
ancestor,
following,
preceding).
Functions
Not all of the built-in functions of XPath are supported in IE5. The most notable
difference is the last() function which is called end()
in IE5. Also, many functions are not supported at all. Here is a full list of
the supported functions in IE5:
attribute() returns all attribute
nodes of the context node.
cdata()
returns all CDATA nodes that are children of the
context node.
comment() returns all comment
nodes that are children of the context node.
date() casts a value to date format.
element() returns all elements that
are children of the context node.
end() is synonymous to last()
in the XPath recommendation.
index() returns the index number of
the node within its parent.
node() returns all nodes (except attributes
and the root node) that are children of the context node.
nodeName() returns the tag name (includes
namespace prefix).
nodeType() returns a number indicating
the node type.
number() casts values to number format.
pi() returns all processing instruction
nodes that are children of the context node.
text() returns all nodes that represent
a text value, that are children of the context node. This includes both text
nodes and CDATA
nodes.
textnode() returns all text
nodes that are children of the context node.
value() returns the value of an element
or attribute.
Examples
In the source code download, you will find a small Visual Basic application, called XPathTester.vbp, which allows you to both practice the writing of XPath queries
and test their performance. If you start the application, you will see this
form:
The Query
tester frame can be used once an XML document is loaded. After loading such a
document (take a big one like Macbeth.xml),
you can see the structure of the document in the tree view control to the left.
If you select a node and type an XPath expression in the Query
text box, you can execute this query, using the selected node as your context
node. All matching nodes are listed in the list box. If you click a list item,
the underlying XML source is shown in the text box on the right. Note that the
number of seconds needed for performing the query is shown directly under the
list box. Use this application to practice writing queries. Notice how more
specific queries have a better performance than very general ones. Also, queries
that specify the structural relations of elements are much faster than queries
specifying the text content of elements and attributes.