The ideal is that a document is just an abstract idea, a structure of information that has no specific visual representation, but has meaning and format. The presentation of such a document should be controlled separately, through a mechanism that takes this abstract representation of the document and transforms it into something you can actually see. This concept has many advantages. We have already seen how dealing with documents as structures of information has helped us author Web pages.
Information is easy to store, edit, find and retrieve if it is organized in a certain canonical way.
In other words, the computer in front of you, being the stupid thing that it is, cannot help you find a document with a certain title unless the author of the document has told his computer that that little line of text at the top is not just a line of text, it is also a title. What you don't know yet is how to control the presentation of these documents so that they appear pretty and meaningful to humans as well as machines. In other words, this is the first tutorial that is actually homo sapiens-biased. The documents we have created so far can be viewed with any Web browser worth its salt. Displaying HTML documents is a Web browser's primary function.