Overview of HTML and CSS

Chapter 1

Overview of HTML and CSS

HTML (Hypertext Markup Language) is continually evolving. Within the past year and a half, two major innovations have extended HTML: an entirely new language for controlling style, and an object model for adding behavior and dynamism to documents. Dynamic HTML in Microsoft Internet Explorer 4.0 encompasses not only the object model for manipulating the document, but also many of the latest HTML and CSS (Cascading Style Sheets) recommendations and working drafts from the W3C (World Wide Web Consortium).

This chapter introduces some of the recent innovations to HTML and CSS supported by Microsoft Internet Explorer 4.0. The combination of existing HTML features and these new innovations with the Dynamic HTML object model allows you to create interactive Web pages and Web applications. This chapter is not a comprehensive review of HTML and CSS—the effective use of HTML and CSS is a topic for an entire book. Rather, this chapter lets you, the Web author, familiarize yourself with the latest work in these areas.

The following topics are covered in this chapter:

• New HTML features This section introduces some of the new features that will be included in the next version of HTML. This next version of HTML, HTML 4.0, is being designed by the W3C and its members. By the time you read this book, the HTML 4.0 recommendation by W3C will probably be final. This section also introduces HTML features supported by Internet Explorer 4.0 that go beyond HTML 4.0.

• Cascading Style Sheets The intent of SGML (Standard Generalized Markup Language), and therefore of HTML, is to separate contents from presentation. This separation was not possible before the introduction of CSS, when tags such as <B> and <FONT> were incorporated in HTML to indicate how content was to be presented. These tags violate the fundamentals of a structured document by allowing the presentation to be embedded in the contents.

  This section introduces the CSS language and its relationship to the recent scripting additions. CSS is a static representation for adding style to a document, but through the object model extensions, that style can be dynamically changed. For example, the style of text can be changed based on the user's environment.

• Examining an HTML DTD HTML is a structured language with a formal definition. This section discusses the importance of the DTD (document type definition) that defines HTML. The HTML DTD is the SGML declaration of the HTML language. A DTD defines the supported set of elements and their attributes and specifies whether an element can contain other elements. Unfortunately, the majority of pages on the Web violate the HTML DTD. With the addition of an object model that exposes the entire page to scripting, ensuring consistent and rational behavior by creating properly structured documents takes on greater importance. In this section, you'll learn how to read a DTD and use it to create valid HTML documents.

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