Introduction to HTML

Historical

The HTML was developed with the Web, in 1989. Tim Berners-Lee wrote it to aswer to the needs of the system he had just invented with Robert Caillau: the World Wide Web.

This language was designed to work with the HTTP protocol. HTML and HTTP constitutes the core the Berners-Lee's invention: a simple and effective way to access documents together thanks to hyperlinks over a network. From now on, we go from one document to another with a simple mouse click: written in HTML, they are transported to the final reader thanks to HTTP.

However, HTML is not the first language with hyperlinks capabilities. Indeed, in 1987, HyperCard made it possible to "surf" through documents using images. Besides, the first works about hyperlinks dated from the 40's (see the Web history).

Goal of HTML

HTML: a text formatting language

At the time Berners-Lee was likely to invent the Web, most people user TeX and PostScript, and seldome SGML, to write their documents. Actually, Tim Berners-Lee realized these languages could not answer the needs of his system. He then invented HTML.

HTML is a simple language used to format simply text documents intended to be displaid first of all on screens. This is the very first purpose of HTML. HTML was not really designed for print rendering; this kind of extra features were developed as the different versions of the language advanced. For instance, it is now possible to render HTML pages with audio tools. But finally, XML is what will make HTML universal.

Contrary to XML whose goal is clearly to separate content and presentation (page layout) of documents, HTML (completed later with style sheets) directly formats the content of documents. The text document contains HTML elements that handle the text layout.

The HTML tags

The page layout is set with what we call tags. Tags are sequences of ASCII characters that have a special meaning and that are entitled to interpretation by Web agents. When we look at the content of an HTML page, it is very easy to recognize HTML tags: they are special portions of text such as this one:

An HTML tag starts with a < and ends with a >. Some tags must be closed (in the example above, <B>...</B>), and some must not (for instance <BR> that codes line breaks). In the latest versions of HTML, there are about 90 tags. Most of them are used to format the documents (bold text, tables...), but few have another role. For instance, it possible to add information about the document (information that won't be displaid), insert an image, Flash animations, JavaScript sequences...

HTML, SGML and XML

HTML is maybe the most famous and used markup language (language that uses tags). However markup languages are older. FOr instance, HTML is a subset of SGML (Standard Generalized Markup Language). SGML is the most general markup language. In the same way, XML (eXtensible Markup Language) is also a subset of SGML.

XML is being more and more used because it makes it possible to write universal documents, because it separates the content and the presentation. It is a sort of metalanguage we can use to define other tags and languages. On the contrary, HTML is a "freezed" language, insofar as the meaning of its tags is predefined. XML tags are not specified, they just have a defined format, and moreover they are different from HTML tags. Finally, HTML and XML are really different and it is impossible to describe HTML in its current state with XML.

Given the power of XML and the popularity of HTML, it is important to be able to describe HTML with XML. Therefore, the W3C has developed XHTML (eXtensible HTML). It is simply HTML tags written the XML way. This orientates the future works about HTML: from now on, HTML can be considered as a real subset of XML, and this equiped HTML with the XML capabilities, and finally, HTML pages are becoming universal. It is then possible to print, read or listen to HTML pages.

 printable format