morespicy

Standard Generalized Markup Language (SGML) is the basis for HTML. Actually, HTML is a subset of SGML. What you probably didn’t realize is that HTML is actually specified in SGML. In other words, SGML is used to define HTML. SGML uses document type definitions (DTDs) to specify itself, the elements of HTML, and
XML. (DTDs are covered in detail in Chapter 6.)

SGML became standard in 1988, when it was approved by the International Standards Organization (ISO). Why should you care? You will better understand where HTML is going if you understand where it came from. Briefly then, SGML is a standard for electronic document exchange. It was, in fact, used in the publication of this book! How does SGML work? When you read a book manuscript, each element on the page (paragraph, section heading, block quote) has its own typographical convention.

For example, in this book, anything representing HTML code appears in courier font, such as the previous HTML code. The publisher communicates to the printer that the code sample should be typeset a certain way by marking up the text with special codes and then telling the printer that whenever he sees those codes, he should change the font to the appropriate font for that element (the publisher gets to define this).

If you’ve ever tried to write your own Web page, you’ve noticed you can’t always get it to look precisely the way you want. Why is that? You are like the publisher: You mark up your text and tell the printer how you want it to look. The browser is like an arrogant printer, who reads what you have to say and, sometimes, does it his own way despite your instructions.

As a Web-page designer, you are at the mercy of the browser. If a publisher doesn’t like the way the printer follows directions, he can take his business elsewhere. If you don’t like the way a particular browser handles your Web page, you can’t do much about it. Fortunately, this is changing with HTML 4.