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Developing Your Site For Performance : Markup/CSS Optimization

Thomas A. Powell and Joe Lima
Expert Author
Published: 2004-11-17

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This is the second part of a five part article. Read part 1 here.

Typical markup is either very tight, hand-crafted and standards-focused, filled with comments and formatting white space, or it is bulky, editor-generated markup with excessive indenting, editor-specific comments often used as control structures, and even redundant or needless markup or code. Neither case is optimal for delivery. The following tips are safe and easy ways to decrease file size:

1. Remove white space wherever possible

In general, multiple white space characters (spaces, tabs, newlines) can safely be eliminated, but of course avoid changing <pre>, <textarea>, and tags affected by the <white-space> CSS property.

2. Remove comments

Almost all comments, save for client-side conditional comments for IE and doctype statements, can be safely removed.

3. Remap color values to their smallest forms

Rather than using all hex values or all color names, use whichever form is shortest in each particular case. For example, a color attribute value like #ff0000 could be replaced with red, while lightgoldenrodyellow would become #FAFAD2.

4. Remap character entities to their smallest forms

As with color substitution, you can substitute a numeric entity for a longer alpha-oriented entity. For example, È would become È. Occasionally, this works in reverse as well: ð saves a byte if referenced as ­. However, this is not quite as safe to do, and the savings are limited.

5. Remove useless tags

Some "junk" markup, such as tags applied multiple times or certain tags used as advertisements for editors, can safely be eliminated from documents.

CSS Optimizations

CSS is also ripe for simple optimizations. In fact, most CSS created today tends to compress much harder than (X)HTML. The following techniques are all safe, except for the final one, the complexities of which demonstrate the extent to which client-side Web technologies can be intertwined.

6. Remove CSS white space

As is the case with (X)HTML, CSS is not terribly sensitive to white space, and thus its removal is a good way to significantly reduce the size of both CSS files and <style> blocks.

7. Remove CSS comments

Just like markup comments, CSS comments should be removed, as they provide no value to the typical end user. However, a CSS masking comment in a <style> tag probably should not be removed if you are concerned about down-level browsers.

8. Remap colors in CSS to their smallest forms

As in HTML, CSS colors can be remapped from word to hex format. However, the advantage gained by doing this in CSS is slightly greater. The main reason for this is that CSS supports three-hex color values like #fff for white.

9. Combine, reduce, and remove CSS rules

CSS rules like font-size, font-weight, and so on can often be expressed in a shorthand notation using the single property font. When employed properly, this technique allows you to take something like

p {font-size: 36pt;
font-family: Arial;
line-height: 48pt;
font-weight: bold;}


and rewrite it as

p{font:bold 36pt/48pt Arial;}

You also may find that some rules in style sheets can be significantly reduced or even completely eliminated if inheritance is used properly. So far, there are no automatic rule-reduction tools available, so CSS wizards will have to hand-tweak for these extra savings. However, the upcoming 2.0 release of the w3compiler will include this feature.

10. Rename class and id values

The most dangerous optimization that can be performed on CSS is to rename class or id values. Consider a rule like

.superSpecial {color: red; font-size: 36pt;}

It might seem appropriate to rename the class to sS. You might also take an id rule like

#firstParagraph {background-color: yellow;}

and use #fp in place of #firstParagraph, changing the appropriate id values throughout the document. Of course, in doing this you start to run into the problem of markup-style-script dependency: If a tag has an id value, it is possible that this value is used not only for a style sheet, but also as a script reference, or even as a link destination. If you modify this value, you need to make very sure that you modify all related script and link references as well. These may even be located in other files, so be careful.

Changing class values is not quite as dangerous, since experience shows that most JavaScript developers tend not to manipulate class values as often as they do id values. However, class name reduction ultimately suffers from the same problem as id reduction, so again, be careful.

Note: You should probably never remap name attributes, particularly on form fields, since these values are also operated on by server-side programs that would have to be altered as well. Though not impossible, calculating such dependencies would be difficult in many Web site environments.

To be continued...

*Originally published at Port80Software.com

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About the Author:
Thomas Powell is founder of PINT, Inc. and a lecturer in the Computer Science department at University of California San Diego. His articles have appeared in serveral magazines and sites, including Network World, Internet Week and ZDNet. He has also published numerous books on Web technology and design, including the best-selling Web Design: The Complete Reference. Visit pint.com.

Joe Lima is the Director of Product Development for Port80 Software. He has worked for a variety of Internet, wireless and software development companies, specializing in research and development for server-centric technologies. Visit port80software.com.

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