Tuesday, November 25, 2008

CSS2 - Cascading Style Sheets Level 2

Introduction to CSS2

This article is not meant to teach you Cascading Style Sheets. If you are looking for a CSS tutorial, you should start with the previous link or try the Free CSS Class. In this article you will learn the basics of CSS2 and how it differs from Cascading Style Sheets, level 1.

Cascading Style Sheets, level 2, supports all of the functionality of CSS1. This means that if you create a CSS1 style sheet, it will work in a user agent that understands CSS2. Plus, the way that CSS1 is written, if you write a CSS2 style sheet, and load it in a CSS1-only user agent, that agent will simply ignore the elements and properties that it doesn't recognize.

Differences Between CSS1 and CSS2

There are some really interesting differences between Cascading Style Sheets level 1 and level 2. CSS2 offers many new options for accessibility and use across various user agents. Positioning in CSS2 is more flexible and offers more options to the designer. Automated content allows developers to force the user agent to display specific content elements as well as the layout, look, and feel. Also there is support for special cursors in CSS2 as well as dynamic outlining.

Accessibility and CSS2

  • Aural style sheets
    With CSS2, there are now style properties to define an aural style sheet for your documents. This means, that if a customer comes to your Web page with a screen reader that is CSS2 enabled, you can define how your page will sound. And this isn't just useful for blind customers, with aural CSS your documents can be listened to in automobiles, as auditory documentation for training, entertainment, and even for people who simply can't read.
  • Paging
    CSS1 dealt almost solely with "continuous media" - that is, media like Web pages that would run continuously until the end. Paged media, such as paper, slide shows, or transparencies were not handled. But with CSS2, it is possible to define how pages should be displayed or printed. This means that you can specify the size of the page to be printed, add things like crop marks and register marks, or how the page should layout on double- and single-sided printings.
  • Media Types
    CSS2 media types allow you to specify different style rules depending upon how your document is going to be displayed. There are many different types you can specify, including: aural, braille, handheld, screen, print, and tv (plus others).
  • International Accessibility Features
    CSS2 now offers features such as more list styles for international documents, support for bidirectional text, and language-sensitive quotation marks.

Improved Features over CSS1

  • Font selection
    When choosing which font to use, CSS2 offers both the standard "name matching" system that CSS1 uses, plus three other methods for defining fonts. These are: intelligent font matching, where the user agent uses a font that is the closest match to the requested font. Font synthesis, where the user agent creates a font that matches the metrics of the requested font. And font download, where the user agent retrieves a font over the Web.
  • Tables
    CSS2 recognizes that there might not be a table element (and related elements) in an XML document - but to display tabular data, it is important to have this as a style. So CSS2 allows you to define any element as a table element (and all the related table elements).
  • Positioning
    While CSS1 had some aspects of positioning, CSS2 takes it to the next level. Relative and absolute positioning determine their location based on their placement within the document or based on the user agent. But along with absolute positioning is the concept of fixed positioning. This acts as a sort of "watermark" in continuous media. In paged media, an element with fixed position is repeated on every page. This allows you to create frame-like documents or place a signature on every page of a document.
  • Cursors
    Now you can define how you want your cursor to respond to various actions. For example, you might want the default behavior over a link to be changed over some of the links in your document. With CSS2 you can define how the cursor should look over any element.

There are many other features that are new with CSS2, but these are some of the most exciting ones. There are also elements like text-shadows, new pseudo-classes, the use of system colors, and dynamic outlines. You can find out more about the differences between CSS1 and CSS2 on the W3C Web site.

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