For nearly two decades the Cascading Style Sheets (CSS) standard has been used to control the presentation of web pages. HTML defines what something is: a heading, a paragraph, an address, an image, etc. CSS describes how that element is presented to the user, including such qualities as its color, border, and dimensions. CSS includes presentational controls that few web designers even consider, such as the way text-to-speech services pronounce web page content.
All of the original presentational rules of CSS were designed for static content; that is, HTML elements that did not change over time. Until recently, if ...