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Appendix A. CSS Resources


General Information
Tips, Pointers, and Other Practical Advice
Online Communities
Bug Reporting

There are a number of very good CSS-related resources available on the Web. Here are some of them.

A.1. General Information

These resources provide a good overview of what's happening in the world of CSS or otherwise provide you with a broad look at CSS.

A.1.1. CSS Recommendations

When all else fails, you can always use the source, Luke. The specifications contain, albeit in a somewhat terse and not always easily decipherable form, the complete description of how conforming user agents should handle CSS. They also contain a complete CSS parsing grammar and forward-compatible parsing rules, both of which are invaluable to the people who write user agents but of minimal interest to almost everyone else.

A.1.2. W3C CSS Activity Page

This is, officially speaking, the online center of the CSS universe. There are links to the CSS Recommendations, to new ideas under consideration, and to other sites about CSS. There are links to historical style sheet proposals, to information about current usage and implementations of CSS, and more. There are also lists of books about CSS, news of new CSS tools, and many other useful bits of information.

A.1.3. W3C CSS Test Suite

This presents a fairly complete set of pages designed to test any CSS implementation. Each page of the suite tests various aspects of CSS properties, one property per page. The tests were largely developed by the author of this book, Håkon Lie (Opera Software), and Tim Boland (NIST), with many contributions from the CSS community and even the browser vendors themselves. If you're wondering how good your browser is at handling CSS1, this is the place to find out. As of this writing, the Test Suite covers only CSS1, but a CSS2 Test Suite is expected in the near future.

A.1.4. Error Checkers

You can save a lot of time and effort simply by running your CSS through a validity checker. This is particularly recommended if you're thinking about asking for help online, because if your CSS contains errors, the first thing the experts will tell you to do is to use a validator. May as well get into the practice first.

A.1.4.1. W3C CSS Validator

If you're having trouble getting your style sheets to work, it might be the result of a typographical error, or some other basic error that is difficult to diagnose. You could spend a long time combing through your styles, exhaustively checking each rule for correctness -- and that's a good exercise, of course -- but you could also have a program do it for you, and simply tell you if it found any errors. The W3C CSS Validator will do exactly that. You can supply it with the URL of a style sheet or document containing styles, or simply paste a block of styles into an

It seems like a reasonable amount of space, so we go with it. Wecheck the result in Figure 11-5, which is basedaround this skeleton markup:

Figure 11-5

Figure 11-5. Final results

There are a few subtle differences from the original layout, butoverall, no significant changes in the document's presentation.We can be quite pleased with the results -- and better still,management will never notice the difference.

input field, and let the validator tell you if your problems are the result of a misspelled color name (or something similar). The chief drawback, for most people, is the technical nature of its reporting. Unless you're already familiar with HTML and CSS, the results you get back may be somewhat confusing.

A.1.4.2. WDG CSScheck

Similar in nature to the W3C's validator, CSScheck offers much friendlier error messages, which makes it more useful to the beginning author. In addition to indicating the severity of the error with whimsical icons (American-style traffic signals, at last check), CSScheck provides a message detailing each problem, as well as the reason it is a problem. It is possible to learn a great deal about good document authoring practices simply by running a few style sheets through CSScheck and carefully reading its responses.

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Now let's talk about top and bottom padding. In theory, an inline element with a background color and padding could have the background extend above and below the element. Figure 7-61 gives us some idea of what that might look like. The line height isn't changed, of course, but since padding does extend the background, it should be visible, right?

Here's where the famous phrase returns: "there may be implementation-specific limits." User agents aren't required to support this type of effect.

P {margin-left: 3em;}
name="INDEX-1381" />margin-rightIE4 P/P IE5 P/Y NN4 B/B Op3 Y/-

This sets the size of the right margin of an element. Negative values are permitted, but caution is recommended.

margin-topIE4 P/P IE5 P/Y NN4 P/P Op3 Y/-

This sets the size of the top margin of an element. Negative values are permitted, but caution is recommended.


you prefer, overlapped), the distance between the end of theLI and the beginning of the H1is 28 pixels, as shown in
Figure 7-17.

Figure 7-17

Figure 7-17. Collapsing in detail

This collapsing behavior only applies to margins. Padding andborders, where they exist, are never collapsed by anything.

also allows browsers to set a minimum value forwidth, below which a block-level element'swidth cannot drop. The value of this minimum canvary between browsers, as it is not defined in the specification. Using auto

If only one of width ,margin-left, or margin-right is

However, it's hardly ever desirable to nest comments, so this limitation is no big deal.

If you wish to place comments on the same line as markup, then you need to be careful about how you place them. For example, this is the correct way to do it:

H1 {color: gray;}   /* This CSS comment is several lines */
H2 {color: silver;} /* long, but since it is alongside */
P {color: white;}   /* actual styles, each line needs to */