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10.5. Adapting to the Environment

CSS2 offers the ability to both alter the browser's environment and integrate its look more closely to that of the user's operating system.

10.5.1. Cursors

To achieve the former, we have the cursor property, which lets you declare what shape the browser's cursor will take as it passes over a given element. Want to make a humorous point about download times? Change the cursor to the wait cursor (an hourglass or watch) when the cursor passes over hyperlinks. You can even hook this property up to "cursor files" (which are not defined by the specification), so you could theoretically class your anchors based on where they go and load different icons for each type of link. For example, off-site links could cause the cursor to change into a globe, while links intended to provide help could trigger a question-mark cursor.

10.5.2. Colors

In order to let web pages more closely match the user's desktop environment, there are a whole list of new color keywords like button-highlight, other hand, the CSS2 property z-index makes this reasoning more complicated. As of this writing, implementations have not yet advanced sufficiently to test this out, and the CSS2 description of z-index doesn't really shed any light on this subject.

Ultimately, if you use negative margins, you may not get the same results from all browsers. Since no one can clearly say which is right, none of them can really be considered to be buggy -- at least, not until the specification is three-d-shadow, and gray-text. These are all intended to use the colors of the user's operating system. In all, there are 27 of these new color keywords. I won't list them all out here, but they're listed in Table 10-1, found at the end of this chapter.

10.5.3. Outlines

While you're moving your cursor around, you might want to show where the focus is set. For example, it might be nice to define a button so that it gets a red box around it when the cursor moves over it. Well, there a number of outline properties, including outline, outline-color, outline-style, and outline-width. To use the example of a red box, you might declare:

IMG.button:hover {outline: solid red 1px;}

This should have the effect described. The outline styles could also be used to set a visible outline for regions in a client-side image map.



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In order to create applications of this category, you might have to define a DTD for your information. Then you have to write classes to import and export information from your XML document(s) (validating using your application's DTD if you have one). You must also write the classes which create the user interface in your application. The user of your application can view and modify information using the GUI (graphical user interface), and they can save (and load) their information to (and from) an XML file (that might use your DTD); in other words, they can save (and load) their information to (and from) an ApplicationML file (where Application is the name of your application). Some examples are AddressBookML, MathML, SVGML, etc.

The classes that import and export information from your ApplicationML file must use the parser and SAX or DOM API in order to import the information. These classes can access this information by using one of the following strategies:

  1. Use DOM to directly manipulate the information stored in the document (which DOM turns into a tree of nodes). This document object is created by the DOM XML parser after it reads in the XML document. This option leads to messy and hard-to-understand code. Also, this works better for document-type data rather than just computer generated data (like data structures and objects used in your code).
  2. Create your own Java object model that imports information from the XML document by using either SAX or DOM. This kind of object model only uses SAX or DOM to initialize itself with the information contained in the XML document(s). Once the parsing and initialization of your object model is completed, DOM or SAX isn't used anymore. You can use your own object model to accessed or modify your information without using SAX or DOM anymore. So you manipulate your information using your own objects, and rely on the SAX or DOM APIs to import the information from your ApplicationML file into memory (as a bunch of Java objects). You can think of this object model as an in-memory instance of the information that came was "serialized" in your XML document(s). Changes made to this object model are made persistent automatically, you have to deal with persistence issues (ie, write code to save your object model to a persistence layer as XML).