HTML and CSS Reference
Figure 3-4. Document structure in HTML5
The new structuring elements of HTML5 can be summarized as follows:
article : Articles, blog posts, forum posts, and so on
aside : Sidebars, such as cross-references to an article
section : Group of elements (typically with a header and a footer )
header : The header of a section (usually with a title and maybe a short overview)
footer : Footer information of the entire page or a part of it (consequently, there might be
more footer tags in a page)
nav : Navigation elements
While useful, not all these structuring elements can be used on all web pages as they are not always suitable for
Document Type Declaration
The various markup language versions have different features that should be handled differently. As discussed earlier,
elements of one document type are not always allowed in others so the appropriate rendering strongly relies on the
identification of the document type being used.
The document type must be declared in the top of the document that associates it with a formally defined
specification. The document type declaration can be defined by a Formal Public Identifier ( FPI ) and the URI of the
so-called Document Type Definition ( DTD ). These URIs are used for identification, and they are not hyperlinks. This is
a machine-readable way to express “this document is HTML” or “this document is XHTML.” Most DTD driver files are
provided by the World Wide Web Consortium.
An FPI is a human-readable, descriptive name that identifies the HTML version, while the DTD defines the
location of the .dtd file (machine-readable grammar) on the W3C server (this file specifies the rules the document
type should follow).