{"rowid": 136, "title": "Making XML Beautiful Again: Introducing Client-Side XSL", "contents": "Remember that first time you saw XML and got it? When you really understood what was possible and the deep meaning each element could carry? Now when you see XML, it looks ugly, especially when you navigate to a page of XML in a browser. Well, with every modern browser now supporting XSL 1.0, I\u2019m going to show you how you can turn something as simple as an ATOM feed into a customised page using a browser, Notepad and some XSL.\n\nWhat on earth is this XSL?\n\nXSL is a family of recommendations for defining XML document transformation and presentation. It consists of three parts:\n\n\n\tXSLT 1.0 \u2013 Extensible Stylesheet Language Transformation, a language for transforming XML\n\tXPath 1.0 \u2013 XML Path Language, an expression language used by XSLT to access or refer to parts of an XML document. (XPath is also used by the XML Linking specification)\n\tXSL-FO 1.0 \u2013 Extensible Stylesheet Language Formatting Objects, an XML vocabulary for specifying formatting semantics\n\n\nXSL transformations are usually a one-to-one transformation, but with newer versions (XSL 1.1 and XSL 2.0) its possible to create many-to-many transformations too. So now you have an overview of XSL, on with the show\u2026\n\nSo what do I need?\n\nSo to get going you need a browser an supports client-side XSL transformations such as Firefox, Safari, Opera or Internet Explorer. Second, you need a source XML file \u2013 for this we\u2019re going to use an ATOM feed from Flickr.com. And lastly, you need an editor of some kind. I find Notepad++ quick for short XSLs, while I tend to use XMLSpy or Oxygen for complex XSL work. \n\nBecause we\u2019re doing a client-side transformation, we need to modify the XML file to tell it where to find our yet-to-be-written XSL file. Take a look at the source XML file, which originates from my Flickr photos tagged sky, in ATOM format.\n\nThe top of the ATOM file now has an additional instruction, as can been seen on Line 2 below. This instructs the browser to use the XSL file to transform the document.\n\n\n\n\n\nYour first transformation\n\nYour first XSL will look something like this:\n\n\n\n\t\n\n\nThis is pretty much the starting point for most XSL files. You will notice the standard XML processing instruction at the top of the file (line 1). We then switch into XSL mode using the XSL namespace on all XSL elements (line 2). In this case, we have added namespaces for ATOM (line 4) and Dublin Core (line 5). This means the XSL can now read and understand those elements from the source XML. \n\nAfter we define all the namespaces, we then move onto the xsl:output element (line 6). This enables you to define the final method of output. Here we\u2019re specifying html, but you could equally use XML or Text, for example. The encoding attributes on each element do what they say on the tin. As with all XML, of course, we close every element including the root.\n\nThe next stage is to add a template, in this case an as can be seen below:\n\n\n\n\t\n\t\n\t\t\n\t\t\t\n\t\t\t\tMaking XML beautiful again : Transforming ATOM\n\t\t\t\n\t\t\t\n\t\t\t\t\n\t\t\t\n\t\t\n\t\n\n\nThe beautiful thing about XSL is its English syntax, if you say it out loud it tends to make sense. \n\nThe / value for the match attribute on line 8 is our first example of XPath syntax. The expression / matches any element \u2013 so this will match against any element in the document. As the first element in any XML document is the root element, this will be the one matched and processed first.\n\nOnce we get past our standard start of a HTML document, the only instruction remaining in this is to look for and match all elements using the in line 14, above.\n\n\n\n\t\n\t\n\t\t\n\t\n\t\n\t\t

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\n\t\n\n\nThis new template (line 12, above) matches and starts to write the new HTML elements out to the output stream. The does exactly what you\u2019d expect \u2013 it finds the value of the item specifed in its select attribute. With XPath you can select any element or attribute from the source XML. \n\nThe last part is a repeat of the now familiar from before, but this time we\u2019re using it inside of a called template. Yep, XSL is full of recursion\u2026\n\n\n\t

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\n\n\nThe which matches atom:entry (line 1) occurs every time there is a element in the source XML file. So in total that is 20 times, this is naturally why XSLT is full of recursion. This has been matched and therefore called higher up in the document, so we can start writing list elements directly to the output stream. The first part is simply a

with a link wrapped within it (lines 3-7). We can select attributes using XPath using @. \n\nThe second part of this template selects the date, but performs a XPath string function on it. This means that we only get the date and not the time from the string (line 9). This is achieved by getting only the part of the string that exists before the T. \n\nRegular Expressions are not part of the XPath 1.0 string functions, although XPath 2.0 does include them. Because of this, in XSL we tend to rely heavily on the available XML output. \n\nThe third part of the template (line 12) is a again, but this time we use an attribute of called disable output escaping to turn escaped characters back into XML. \n\nThe very last section is another call, taking us three templates deep. Do not worry, it is not uncommon to write XSL which go 20 or more templates deep!\n\n\n\t\n\t\t\n\t\t\t\n\t\t\t\ttag\n\t\t\t\n\t\t\t\n\t\t\t\t\n\t\t\t\n\t\t\t\n\t\t\n\t\t \n\t\n\n\nIn our final , we see a combination of what we have done before with a couple of twists. Once we match atom:category we then count how many elements there are at that same level (line 2). The XPath . means \u2018self\u2019, so we count how many category elements are within the element. \n\nFollowing that, we start to output a link with a rel attribute of the predefined text, tag (lines 4-6). In XSL you can just type text, but results can end up with strange whitespace if you do (although there are ways to simply remove all whitespace). \n\nThe only new XPath function in this example is concat(), which simply combines what XPaths or text there might be in the brackets. We end the output for this tag with an actual tag name (line 10) and we add a space afterwards (line 12) so it won\u2019t touch the next tag. (There are better ways to do this in XSL using the last() XPath function). \n\nAfter that, we go back to the element again if there is another category element, otherwise we end the loop and end this .\n\nA touch of style\n\nBecause we\u2019re using recursion through our templates, you will find this is the end of the templates and the rest of the XML will be ignored by the parser. Finally, we can add our CSS to finish up. (I have created one for Flickr and another for News feeds)\n\n\n\nSo we end up with a nice simple to understand but also quick to write XSL which can be used on ATOM Flickr feeds and ATOM News feeds. With a little playing around with XSL, you can make XML beautiful again.\n\nAll the files can be found in the zip file (14k)", "year": "2006", "author": "Ian Forrester", "author_slug": "ianforrester", "published": "2006-12-07T00:00:00+00:00", "url": "https://24ways.org/2006/beautiful-xml-with-xsl/", "topic": "code"}