Back to 90s when HTML 4 appeared, the W3C decided that structure and formatting instructions should be added to the same document with HTML code in order to make it more powerfull. Then the idea begun: a new passion in web publishing, where formatting instructions could be saved seperately from the content and could be applied to an entire Web site. In HTML 4 most of the formatting elements where marked as deprecated by W3C, which means that it is preferable for web designers not to use them. At that time CSS (Cascading Style Sheets) were born to fill the gap between content and appearance. CSS 1 were limited to recreating HTML effects. In 1998 comes out the the second version of CSS (CSS 2) with much more capabilities, like position rules, which lead to much more professional and nice-looking web pages. The problem was that each browser understood the rules in a different way, which lead to a confused situation. The solution was to rewrite HTML in XML (eXtensible Markup Language), which is much more powerfull and provides structure. The result is XHTML which has all the features of HTML (so it can be understood by any browser) and the power and flexibility of XML. XHTML is the perfect foundation for CSS. It formats the basic structure and CSS defines the appearance. CSS 2 are almost supported by any browser now. CSS rules are saved in text files. They can be written in the same file as the (X)HTML code or in a seperate one, which makes them more flexible as they can be applied to an entire Web site at once. XHTML unleashed the power of CSS and showed the way for more recent trends like RSS (which is the content without the formatting).
