XPointer Basics - Proof Of The Pudding (
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By combining the axis and node
test into a location step, and combining multiple location steps into a location
path, it becomes possible to locate specific nodes with the document tree quite
easily. Using the following XML sample, let's consider some examples.
<?xml version="1.0"?>
<movie id="67" genre="sci-fi">
<title>X-Men</title>
<cast>Hugh
Jackman, Patrick Stewart and Ian McKellen</cast>
<director>Bryan Singer</director>
<year>2000</year>
<?play_trailer?>
</movie>
The path
/child::movie/child::cast/child::text()
references the text node
Hugh Jackman, Patrick Stewart and Ian McKellen
In order to make this a little easier to read (and write), XPath assumes a default
axis of "child" if none is specified - which means that I could also write the
above path as
/movie/cast/text()
The * character matches all child elements of the context node, while the @ prefix
indicates that attributes, rather than elements, are to be matched. The path
/movie/*
would match all the children of the "movie" element, while the path
/movie/@*
would refer to all the attributes of the movie element. In case I need a specific
attribute - say, "genre", I could use the path
/movie/@genre
or the path
/movie/attribute::genre
both of which would reference the value
sci-fi
Finally, the path
/*
would reference the first element under the document root, which also happens
to be the outermost element, while the path
//*
selects all the elements in the document.
So far as constructing basic XPointers go, the material above is more than sufficient
for your needs. However, if you'd like to learn more about XPath's capabilities,
including its built-in functions and expressions, take a look at the XPath tutorial
at the XPath specification at http://www.w3.org/TR/xpath.html.
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