then its background should be transparent so that the background of its ancestor elements will be visible. Imagine for a moment that the default value were something else, such as silver. Then you would always see something along the lines of Figure 6-16. This could be quite a problem, if that's how browsers behaved! Fortunately, they don't.

Figure 6-16

Figure 6-16. Nontransparent backgrounds

Most of the time, you'll have no reason to use the keyword transparent. On occasion, though, it can be useful. Although it's the default value, users might set their Tuesday 03rd of May 2016 01:10:30 AM

by Eric A. Meyer
ISBN 1-56592-622-6
First edition, published May 2000.
(See the
catalog page for this book.)

Search the text of Cascading Style Sheets: The Definitive Guide.

Table of Contents

Copyright Page
Chapter 1: HTML and CSS
Chapter 2: Selectors and Structure
Chapter 3: Units and Values
Chapter 4: Text Properties
Chapter 5: Fonts
Chapter 6: Colors and Backgrounds
Chapter 7: Boxes and Borders
Chapter 8: Visual Formatting
Chapter 9: Positioning
Chapter 10: CSS2: A Look Ahead
Chapter 11: CSS in Action
Appendix A: CSS Resources
Appendix B: HTML 2.0 Style Sheet
Appendix C: CSS1 Properties
Appendix D: CSS Support Chart
Library Navigation Links

Copyright © 2002 O'Reilly & Associates. All rights reserved.

writing, no other browser will recognize :hoverunder any circumstances. :focus

Similarto :hover is :focus, which isused to define styles for elements that are "in focus." A

Client and Server side - Application Servers

The 2nd category of Java applications called Java Application Servers (or app servers) and they make good use of XML. Unlike client side graphical Java apps (from the previous section) which are very standalone in their operations, app servers tie many different networked software components together in order to provide information from multiple sources to a set of client side Java apps or web browsers (maybe even running on different devices). This is shown in Figure 2. An app server is actually a conglomeration of several distributed and client/server software systems. So when you write an app server, you are actually writing many different software systems which are all networked to work together, to process information that comes from various sources, and distribute this information to a set of client apps (that you also have to write) running on different devices and platforms.

How can XML help app servers do their work? As you can see in Figure 2, in order for the app server to harvest information from such a rich variety of sources, there must be some common ground between all of these sources (each of which might be running on a different hardware and software system). This common ground is the information which flows throughout the entire system, regardless of what source the information comes from. CORBA is an example of tying disparate systems together based on the interfaces that certain remote objects implement. XML does the same thing for data. It allows these disparate systems to share information in a medium that consists only of pure information (and the structural relationships that exist inside of that information). By taking the lowest common denominator approach by using plain text to encode data, XML allows these systems to talk with each other without requiring any special binary information format converters or other service layers to translate between binary formats (for encoding data). Also, since HTTP already supports transmission of plain text, it is completely natural to move XML around using the Hyper Text Transfer Protocol through firewalls and disparate networks. This is shown in Figure 3. XML can be transmitted between systems using one of the most prevalent protocols in use today, Hypertext Transfer Protocol or HTTP 1.1 (which is the protocol of the web).

The result is the same, since all we've done is to explicitly declare what was already the case. In other words, there is no way to "turn off " underlining (or overlining or a line-through) within an element. If a decoration has been set for an element, then all of its children will have the decoration applied visually, if not in fact.

Combined with vertical-align, even stranger things will happen. Figure 4-60 shows but one of these oddities. Since the SUP element has