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Asymmetrically Yours - XML

You already know how to link XML documents together with XLink, and isolate specific nodes or node collections with XPath. Now uncover the third and final piece of the XML linking jigsaw - XPointer, an experimental technology from the W3C, which allows you to create XML links to specific points or ranges within an XML document.

TABLE OF CONTENTS:
  1. XPointer Basics
  2. The Need For XPointer
  3. Revolving Around An Axis
  4. Proof Of The Pudding
  5. A Fragmented View
  6. A Range Of Options
  7. Asymmetrically Yours
  8. Linking Up
By: icarus, (c) Melonfire
Rating: starstarstarstarstar / 2
December 12, 2001

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The range() function is great for times when you need to define a range which begins and ends with the same element. However, for situations which require more asymmetric ranges, XPointer also offers the range-to() function, which allows link authors greater flexibility when defining ranges.

The range-to() function creates a range beginning with the context node and ending with the location set specified as an argument to the range-to() function. For example, the following XPointer

xpointer(id('67')/cast/range-to(id('67')/director))
defines a range beginning at the opening "cast" element and ending at the closing "director" element.

It's also possible to identify points and ranges within character data - the string-range() function scans a specified location for a match to a user-specified string, and returns a range containing the result. So, the following XPointer

xpointer(string-range(//cast, "Patrick Stewart"))
would return a range enclosing the string "Patrick Stewart" from the "cast" element.

If the XML document above contained more than one "cast" element matching the specified string, the string-range() function would return multiple ranges, one for each match.

It's possible to further constrain the range returned by specifying two additional arguments to the string-range() function - an offset to push forward the starting point of the range, and a length constraint to move back the ending point. So a modification of the XPointer above to

xpointer(string-range(//cast, "Patrick Stewart", 9, 4))
would return a range enclosing the substring "Stew".

The string-range() function ignores embedded elements - which means that a change to the XML document above to read

<?xml version="1.0"?> <movie id="67" genre="sci-fi"> <title>X-Men</title> <cast>Hugh<space />Jackman,<space />Patrick<space />Stewart<space />and<space />Ian<space />McKellen</cast> <director>Bryan Singer</director> <year>2000</year> <?play_trailer?> </movie>
would not affect the XPointer at all.

Since the string-range() function only returns string ranges, it follows that the start and end points of these returned ranges are always character-points, not node-points.

 
 
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