XSLT Exercise 4: Styling Skyrim

The usual housekeeping:

Because this document is not in a namespace, we do not need the @xpath-default-namespace attribute, and the only thing we need to add to <oXygen>’s default XSLT stylesheet template is the @xmlns attribute pointing to the HTML namespace. We also add our usual <xsl:output> line that we use when producing HTML (for making sure we produce valid HTML 5 in XHTML format). Here’s what we need:

          <xsl:stylesheet xmlns:xsl="http://www.w3.org/1999/XSL/Transform"
    xmlns:xs="http://www.w3.org/2001/XMLSchema"
    xmlns:math="http://www.w3.org/2005/xpath-functions/math" exclude-result-prefixes="xs math"
    xmlns="http://www.w3.org/1999/xhtml" version="3.0">
    <xsl:output method="xhtml" encoding="utf-8" doctype-system="about:legacy-compat"
        omit-xml-declaration="yes"/>

Overview of the assignment

We will be preparing HTML reading view styled for the web, based on the original XML document. We’re going to work with the <body> element, concentrating on processing the in-line elements to style the text. You can use some of the basic HTML in-line elements, like  for emphasis or  for strong emphasis, but you’ll also want to use CSS to set some elements to different colors or background colors or borders or fonts or font sizes or font styles (e.g., italic) or font weights (e.g., bold) or text decoration (e.g., underlining) or text transformation (e.g., convert to all upper case) … well … anything else. We describe below how to do that.

There are six types of in-line elements in the input XML document:

<QuestEvent>
<QuestItem>
<character>
<epithet>
<faction>
<location>

Some are immediately inside a <paragraph> and some are inside other elements that are inside paragraphs. You may not know at the outset which ones can be inside which other ones, or how deeply they can nest. Happily, with XSLT, unlike with many other programming languages, you don’t need to care about those questions!

How to process richly mixed content

Prose paragraphs with in-line elements that might contain other in-line elements are richly mixed content, with varied and unpredictable combinations of elements and plain text. This is the problem that XSLT was designed to solve. With a traditional procedural programming language, you’d have to write rules like inside this paragraph, if there’s a <QuestEvent> do X, and, oh, by the way, check whether there’s a <QuestItem> or a <location> inside the <QuestEvent>, etc. That is, most programming languages have to tell you what to look for at every step. The elegance of XSLT when dealing with this type of data is that all you have to say inside paragraphs and other elements is, I’m not worried about what I'll find here; just process (apply templates to) all my children, whatever they might be.

The way to deal with mixed content in XSLT is to have a template rule for every element and use it to output whatever HTML markup you want for that element and then, inside that markup, to include a general <xsl:apply-templates/>, not specifying a @select attribute. For example, if you want your <QuestEvent> to be tagged with the HTML  tags, which means strong emphasis and which is usually rendered in bold, you could have a template rule like:

<xsl:template match="QuestEvent">
  <strong>
      <xsl:apply-templates/>
  </strong>
</xsl:template>

You don’t know or care whether <QuestEvent> has any child nodes or, if it does, what they are. Whatever they are, this rule tells the system to try to process them, and as long as there’s a template rule for them, they’ll get taken care of properly somewhere else in the stylesheet. If there are no child nodes, the <xsl:apply-templates/> will apply harmlessly (as there will be nothing to process). As long as every element tells you to process its children, you’ll work your way down through the hierarchy of the paragraph without having to know which elements can contain which other elements or text nodes.

Taking stock: when to use `@select`

In the previous XSLT assignment, where you built HTML tables from XML-coded survey data, you used <xsl:apply-templates select="…"/>, specifying exactly what you wanted to process where. That makes sense when your input (those <fs> and <f> elements and their special attributes) and your output (an HTML table) are very regular in structure. Use the @select attribute when you know exactly what you’re looking for and where you want to put it.

In this assignment, on the other hand, you don’t know (and don’t need to know) the order and nesting hierarchy of whatever tossed salad of elements and plain text you might find inside a paragraph or its subelements. You just want to process whatever comes up whenever it comes up. <xsl:apply-templates/> without the @select attribute says apply templates to whatever you find. The upshot: Omit the @select attribute when you are processing lots of different mixed up alternatives and you do not need to rearrange them. (You can still treat them all differently because you’ll have different template rules to match them, but when you assert that they should be processed, you don’t have to know which ones they actually are.)

Styling your output: HTML and CSS

HTML provides a limited number of elements for styling in-line text, which you can read about at http://www.w3schools.com/html/html_formatting.asp. You can use any of these in your output, but note that presentational elements, the kind that describe how text looks (e.g.,  for italic), are generally regarded as less useful than descriptive tags, which describe what text means (e.g.,  for emphasis). Both of the preceding are normally rendered in italics in the browser, but the semantic tag is more consistent with the spirit of XML than the presentational one.

The web would be a dull world if the only styling available were the handful of presentational tags available in vanilla HTML. In addition to those options, there are also ways to assign arbitrary style to a snippet of in-line text, changing fonts or colors or other features in mid-stream. To do that:

Before you read any further in this page, read our Using  and @class to style your HTML page.
To use the strategies described at that page, create an XSLT template rule that transforms the element you want to style to an HTML  element with a @class attribute. For example, you might transform <faction ref="MythicDawn">assassins</faction> in the input XML to assassins in the output HTML. You can then specify CSS styling by reference to the @class attribute, as described in the page we link to above.
- Note that you can make your transformations very specific. For example, instead of setting all <faction> elements to the same HTML @class, you can create separate template rules to match on factions according to their attribute values. For example, <xsl:template match="faction[@ref='MythicDawn']"> is a normal XPath expression to match <faction> elements only if they have a @ref attribute with the value MythicDawn.
- If you really want to exercise your XPath skills, note that in the header some factions are described (with an @alignment attribute) as evil, good, or neutral. You can write a matching rule that will dereference the @ref attribute on, say, <faction ref="MythicDawn">assassins</faction>, look up whether this is an evil, good, or neutral faction, and set the @class value accordingly. You could make all good factions one color and all evil factions a different color, letting XPath look up the moral alignment of a faction for you. Note: This will require the XSLT current() function, to read a specific value from the source node at the time it is being processed.
Setting the @class attributes in the output HTML makes it possible to style the various  elements differently according to the value of those attributes, but you need to create a CSS stylesheet to do that. Create the stylesheet (just as you‘ve created CSS in the past), and specify how you want to style your  elements. Link the CSS stylesheet to the HTML you are outputting by creating the appropriate <link> element in your output HTML (you can remind yourself how to do that here in this section of our Intro to CSS). You should set that <link> element in your XSLT so it is always output every time you update your code.

When the smoke clears

What you should produce, then, is:

An XSLT stylesheet that transforms the <body> element and its contents into HTML.
The resulting HTML should style the six types of in-line elements listed above. At least some of those styles should be set using  elements with the @class attribute.
You need to create a CSS file, linked to your output HTML, that specifies how to style the output document. You can look up the most useful of the available CSS properties at http://www.w3schools.com/css/. We’d suggesting following the links on the left under CSS styling for styling backgrounds, text, and fonts, as well as the link for borders under CSS box model.

Please upload your XSLT, HTML, and CSS files to Canvas. Remember to link your CSS to the HTML file!