Book HomeCascading Style Sheets: The Definitive GuideSearch this book Thursday 19th of January 2017 01:51:28 PM

10.4. Generated Content

Generated content is a new way of adding things to existing content without having to alter the content itself. It's done by using the pseudo-elements :before and :after and the property content. Here's a basic example of how it works:

P:before, P:after {content: "\""; color: gray;}
<P>This is a quote.</P>

The browser will display what's shown in Figure 10-15.

Figure 10-15

Figure 10-15. Adding generated content

Note that the double-quote mark was escaped out -- that is, preceded by a backslash. This is necessary, since text values for content must be enclosed in double quotes. You could also place images before (or after) content, using something like P:before {content: next. In that case, you'd want to set the first element of each section to prohibit floating elements from appearing next to it. If it might otherwise be placed next to a floated element, it will be pushed down until it appears below the floated image, and all subsequent content will appear after that, as shown in Figure 7-73.

Figure 7-73

Figure 7-73. Displaying an element in the clear

This is done with clear.

clear

url(para.gif);} to put a paragraph symbol at the beginning of each paragraph. You can even string multiple values together like this (shown in Figure 10-16):

P:before {content: url(para.gif) " -- ";}
Figure 10-16

Figure 10-16. Adding an image and text before a paragraph

This would cause each paragraph to be started with a paragraph symbol, a blank space, two dashes, and then another blank space. Note that all of this is considered part of the paragraph and is inlined within it. The spaces appear before and after the double dash because they're included in the string value. If these spaces were omitted, then space would not appear to either side of the dashes.

Let's say, though, that you want to do some real quoting, using real quotation marks -- you know, the curly double quotes that are so hard to specify in HTML and which often don't show up even if you do try to specify them. CSS2 has ways to handle this.

content has some other values you can use:

  • open-quote, which inserts an opening quotation mark

  • close-quote, which inserts a closing quotation mark

  • no-open-quote, which prevent the insertion of an opening quotation mark

  • no-close-quote, which prevent the insertion of an closing quotation mark

So if you wanted your quotations to begin and end with quotation marks, instead of typing in a literal quotation mark, you could let the browser insert "smart quotes" for you.

BLOCKQUOTE:before {content: open-quote;}
BLOCKQUOTE:after {content: close-quote;}

10.4.1. Automatic Numbering

In the same vein, CSS2 also includes properties for automatic numbering. First, you can specify a counter as a value of content. This can be a bit tricky, and it would take too long to run through all the possibilities, but here's an example. Say you wanted the chapters and sections of a document numbered 1, 1.1, 1.2, 1.3, and so on. In addition, you're using H1 for your chapters and H2 for your sections. Here are the declarations you would use:

H1:before {
content: "Chapter " counter(chapter) ". ";
counter-increment: chapter;   /* Add 1 to chapter */
counter-reset: section;       /* Set section to 0 */
}
H2:before {
content: counter(chapter) "." counter(section) " ";
counter-increment: section;
}

As we can see from Figure 10-17, the user agent will add the word "Chapter" and a number at the beginning of H1 text. This number is automatically incremented with each H1, due to the declaration counter-increment: chapter;. It also sets the section counter back to zero through counter-reset: section;. Then, for each section heading (H2), the browser uses the chapter number, followed by a period (.) followed by the current section number, which is also automatically incremented.

Figure 10-17

Figure 10-17. Adding counters to elements

You don't have to increment by one every time, either. You can define any integer as the increment value, including zero and negative numbers. If you want each section to have an even number, as we see in Figure 10-18, then you can declare the following:

H2:before {
content: "Section " counter(section) ". ";
counter-increment: section 2; /* Add 2 to chapter */
}
Figure 10-18

Figure 10-18. Changing a counter's incremental value

You can also keep an element from incrementing a counter by setting its display to none. Of course, that will cause the element to disappear altogether.



Library Navigation Links

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

Since the structure of the XML document can be specified in DTDs they provide a simple way to make it easier to exchange XML documents that conform to a DTD. For example, if two software systems need to exchange information, then if both of the systems conform to one DTD, the two systems can process information from each other. DTDs are not as powerful as some kind of schema architecture for XML, they don't support typing, subclassing, or instantiation mechanisms that a schema architecture must have.

DTDs are a simple way to make sure that 2 or more XML documents are of the same "type". Its a very limited approach to making "typed" XML documents shareable across systems. In the future some kind of schema system will be proposed by the W3C that should allow typing, instantiation and inheritance of information (in XML).

XML enables interoperability

All of the advantages of XML outlined so far all make interoperability possible. This is one of the most important requirements for XML, to enable disparate systems to be able to share information easily.