XPointer Basics - A Range Of Options (
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To the various node types defined in the XPath specification,
XPointer adds two more: points and ranges.
A point is defined as the address of a specific location within an XML document.
It is identified by two characteristics: a container node and an index number.
The container node is the node which encloses the point, while the index number
is an integer which indicates the relative position of the point among the children
of the container node.
There are two types of points: node-points, which refer to XML elements, and
character-points, which refer to the text contained within XML elements.
The index number within a point definition differs in meaning depending on whether
the point is a node-point or a character-point. In the case of a node-point, the
index number references a specific child node or nested XML element; in the case
of a character-point, it references a particular character of the text string.
Points are defined with XPointer's start-point() and end-point() functions, both
of which accept a location path (or collection of location paths) as argument.
A range, defined as the area between two points, is created with the range()
function, which returns a collection containing all the elements within the specified
range.
An example might help to make this clearer. Consider the following XML document:
<?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>
Now, the XPointer
xpointer(range(/))
would return a range covering the / element (the document element) and all those
within it - in other words, a range covering the entire document.
The start and end points of this range would be accessible via the XPointers
xpointer(start-point(/))
xpointer(end-point(/))
and would point to the beginning and end of the document respectively.
In a similar manner, the XPointer
xpointer(range(//movie/title))
would identify the range
<title>X-Men</title>
while the XPointer
xpointer(start-point(//movie/director))
would point to the location immediately preceding the "director" element.
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