#left {
position: absolute;
left: 2%;
width: 22%;
top: 106px;
background-color: #ffffff;
}

#content {
position: absolute;
left: 25%;
width: 50%;
top: 106px;
background-color: #ffffff;
overflow: auto;
}

visible = The element gets expanded to show the entire content.
hidden  = The content will be cut if it overflows.
scroll  = The browser should offer scroll bars.
auto    = The browser should decide how to render the element. Scroll bars are allowed.

#right {
position: absolute;
left: 76%;
width: 22%;
top: 106px;
background-color: #ffffff;
overflow: auto;
}

App server developers are not restricted to using HTTP, they can transmit and recieve XML information using simple remote CORBA objects and RMI objects. The key is that by using XML, it makes these remote services or objects easier to build. And, by sticking with XML, any one of these technologies can be used in your design of your app server. You can use whatever technology is most appropriate to getting the job done, knowing that all the information flows as XML and can be processed by any part of the system. The reason Java object serialization did not achieve this is because it encodes object data to a binary format that is dependent on too many things (like the JVM version, and the existence of classes when things are deserialized, etc). XML is not limited by any of these restrictions (or problems), which makes it much easier to create systems that allow XML information to flow between different subsystems. Also by relying only on the data, large portions of the system can be replaced with better or different implementations for future-readiness.

App servers traditionally give their client apps access to information in remote databases, remote file systems, remote object repositories, remote web resources, and even other app servers. All these information sources don't even need to reside on the machine that hosts the app server. These remote resources may be on other machines on the Intranet or the Internet. Using Java and XML, RMI, JDBC, CORBA, JNDI, Servlet and Swing, you can create app servers that can integrate all kinds of remote and local information resources, and client apps that allow you to remotely or locally access this information from the app server.

In the future, with publicly available DTDs that are standardized for each vertical industry, XML based app servers will become very popular. Also when XML schema repositories become available and widely used, app servers will be able to take on a new role and provide application services that are not offered now. Companies will need to share information with other companies in related fields, and each company might have a different software system in which all their data is housed. By agreeing upon a set of DTDs or schemas (encoded in XML), these companies can exchange information with each other regardless of what systems they are using to store this information. If their app servers can exchange XML documents (based on some shared DTD or schema), then these disparate app servers can understand each other and share information. One of the uses for XML foreseen by the W3C is just this, vertical industries (like insurance and health care) creating sets of DTDs and schemas that all companies in the industry agree upon. Then these companies' app servers can talk to each other using some popular protocol (like HTTP or CORBA/IIOP) to exchange information between each other. This has the potential to save a lot of time and money in the daily business operations of these companies.

Figure 7-70. A floating image with negative top and left margins

The math in this situation works out something like this: assume thetop inner edge of the DIV is at the pixel position100. The browser, in order to figure out where the top inner edge ofthe floated element should be will do this: 100px+ (-15px)it as a number of pixels. See Chapter 8, "Visual Formatting" for adetailed discussion of line-height and line boxes.

Example

P {line-height: 18pt;}H2 {line-height: 200%;}

A shorthand property condensing allother list-style properties. It applies to allelements with a display value of list-item ; inordinary HTML, this is any <LI> element.apply to both the element and the background image.

Figure 6-39. Centering the background image using percentages

In order to understand this concept, let's examine this processin closer detail. When you center a background image in an element,the point in the image which can be described as50% 50% is lined up with thepoint in the element that can be described the same way. This isshown in Figure 6-40.

top: 50%; bottom: 0; left: 50%; right: 0;

In this example, the outer left edge of the positioned element is placed halfway across the containing block. This is its offset from the left edge of the containing block. The outer right edge of the positioned element, however, is not offset from the right edge of the containing block, so the two are coincident. Similar reasoning holds true for the top and bottom of the positioned element: the outer top edge is placed halfway down the containing block, but the outer bottom edge is not moved up from the bottom. This leads to what's shown in Figure 9-2.