To make a site accessible, it is necessary to respect a certain number of simple rules, which will be described in the following pages. Two important principles should be pointed out:
Every visual element should be completed with a textual comment describing it. The comments are then called alternative contents. The «alt» attribute, for example, allows to comment a picture inserted with the «IMG» element. Note that these picture comments are used by the main graphical browsers — when pictures are loading and as a key when the mouse remains longer on a picture.
The structure and layout of the document should be dealt with separately. The structure is specified by the HTML elements and attributes (titles, subtitles, paragraphs, images...), the layout should be specified with style sheets (typographic choices, colours, spacing...). The clear separation of the layout from the content helps the non visual browsers to extract the logical structure of the document more easily. It also provides the authors of visual pages with more flexibility for the page layout (style sheets provide more possibilities than HTML).
The information pages of a site are often made of text essentially, so they are accessible. On the other hand, homepages and navigation pages often contain graphical or dynamic elements which intend to make the site attractive and aesthetic. Those pages should be written with particular attention, because they are often the only pages that prevent access to documents that would be accessible without the first page.
The structure of a printed document can be recognised through its layout. The typography, margins and spacing indicate the different parts and the titles to the reader. These characteristics generally correspond to rules that were implicitly accepted by the reader (for example, the titles are printed in bold text and with larger characters than the rest of the text). In an HTML document, the author uses the HTML elements that are intended to that extend to point out the functions of each part of his document and even of each word or each group of words. For example, the «H1» element will be used to indicate that a group of words builds the main title (the title will be placed between the tags <H1> and </H1>).
During the reading, the browser creates the layout of the document according to the elements that are used. A graphical browser relies most of the time on the rules applied to a printed document (areas which are defined with the «H» element are written with bold characters, which are larger than the rest of the text, and spacing will be inserted before and after the title). A non visual browser shows the same document in a completely different way to meet the user's needs or specific preferences.