Sams Teach Yourself XML in 21 Days

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Sams Teach Yourself XML in 21 Days, 3rd Edition

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Recommended Book

Recommended Book 

Sams Teach Yourself XML in 21 Days, 3rd Edition

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Summary

CSS is a W3C specification, and you can find the W3C recommendations for CSS1 and CSS2 at http://www.w3.org/TR/REC-CSS1 and http://www.w3.org/TR/REC-CSS2; CSS3 is still under development.

Style sheets are collections of style rules, each of which shows how to format an XML element. A rule is made up of a selector, which is the element or elements you want to format, and the rule specification itself, which shows the format.

Today you've seen various ways of creating selectors. You can specify which XML element you want to format directly by name. You can create style classes and use the class attribute in browsers such as Internet Explorer. You can also select elements by ID value.

Rule specifications are made up of CSS property/value pairs in a semicolon-separated list, surrounded by curly braces. There are hundreds of available properties, such as font-weight, text-align, and text-decoration. You can assign values by listing those values after a property name in a rule specification, like this:

{font-weight: bold; text-align: center; text-decoration: underline}

Knowing which CSS properties are available is essential for effective use of CSS formatting. Today's discussion focuses on the CSS properties you can use and what values you can assign to them.

A style sheet rule includes both a selector and a rule specification, like this:

title {display: block; font-size: 36pt; font-weight: bold;
    text-align: center; text-decoration: underline}

One important CSS property is display, which, among other things, lets you create block elements when you assign the value block to it. Block elements are displayed on their own lines. If you don't make an element a block element, it will be an inline element by default; inline elements are arranged by the browser, and they follow the normal flow of items the browser displays. If you want to format elements whose data follows that flow, you should use inline elements. If you want a data item to appear on its own line, you should use a block element.

Today you took a look at text properties, including how to set font face, font size, font weight (such as bold), text alignment, indentation, and decoration (such as underlining and overlining of text). You also saw how to specify colors and backgrounds, as well as how to style borders. And you saw that you can even display images along with your XML data by using CSS properties such background-image and background-repeat.

You can use CSS to position elements, both in absolute and relative terms. This ability to position what you want where you want in a Web page is responsible for much of CSS's popularity among Web page authors. As you've seen, you can position both text and images as you like by using CSS positioning.

Today you also discussed formatting lists and tables by using CSS. This is particularly useful because it helps you format and display data effectively.

After you've created a CSS style sheet, one way of connecting that style sheet to an XML document is by using the <?xml-stylesheet?> processing instruction. Although not an official part of XML, this processing instruction has become an accepted convention. It's important to bear in mind, however, as you use CSS, that different browsers have different levels of support, and the results you get often differ from browser to browser.

As you've seen today, the major HTML browsers are set up to handle and display XML by using CSS, which is a good idea because CSS is in widespread use with HTML. On the other hand, CSS is not an ideal solution for displaying XML data visually because CSS has its own, very non-XML, syntax. There is an XML solution—Extensible Stylesheet Language Transformations (XSLT)—as you'll see tomorrow. XSLT is written in XML, and it lets you target the data in XML documents better than CSS. All the details are coming up tomorrow.