An important aspect of building sustainable, accessible websites is the principle of separating structure and presentation. Applying the principle results in cost cuts, efficient construction and maintenance, and improved recognisability and usability.
This principle is a method of building a website in which web technologies are used in a layered fashion, so that the basic content and functionality of a web page is available to all. If web technology fails or is not supported, the content is provided by the technology below it.
Web builders can use optional technologies such as CSS and client-side scripts, as long as they complement the content: users must still be able to access the content if they do not or cannot use these technologies.
The separation of structure and presentation aka progressive enhancement work best when developing a completely new website. But how can these production philosophies be applied when an existing website needs to be modified?