VI. How To?
6.2. Accessibility Implementation Approach
6.2.2. Progressive Enhancement
As said, progressive enhancement is the opposite approach, and tends to fill the gaps of graceful degradation: “begin with the basic version, then add enhancements for those who can handle them” (Olsson, 2007, p2).
The most important example of progressive enhancement, and certainly the most use, in ignorance of its status, is the use of CSS to manage the presentation of the web page. Indeed, a web page build in strict HTML with a style sheet associated will only use the information contain in the said style sheet if the browsers of the visitors allows it; it the browser does not allows it, the page’s elements will adopt their default behaviour, specified by the browser or by the user.
“Progressive enhancement when it comes to JavaScript is becoming more common these days. The key to this is known as unobtrusive JavaScript. An unobtrusive script is silently ignored by user agents that do not support it, but is applied by more capable devices. Just like an external style sheet” (Olsson, 2007, p2).
The proper use of the AJAX technology, which calls for JavaScript, can be a good example of progressive enhancement; especially in the case of multiple drop-down selection menus (select tag) where the information of the second and following menus can depends on the information selected from the first one, or in the case of auto-completion fields.
The progressive enhancement approach is sometime being criticize because it implies more complex scripts and a different approach of the web page conception (Dimon, 2005), as progressive enhancement concentrate firstly on the structure of the page and then on its “enhancing” presentation.
In an Accessibility point of view, this second approach is preferable to the first one; and in any case any of them is preferable to none. Indeed, progressive enhancement, will add enhancing features to a plain website that is accessible, without damaging its accessibility level. Users that cannot display or use the-said features will not see their navigation blocked and users who can will enjoy them.