Production philosophy: Do not rely on optional technology

A characteristic of a progressively enhanced website is that the visitor can access the content without having to depend on a particular, optional technology.

Therefore, during construction, web developers should presuppose support for optional technology. CSS (Cascading Style Sheets) should not be a prerequisite for a visitor to navigate through the sites, nor should he depend on client-side scripts to be able to complete a form. There is more information on these situations at Cascading Style Sheets and Client-side script and DOM.

This means that web builders can use optional technologies, provided they complement the content and are no prerequisite to access the content.

Do not make the function of the website dependent on optional technology, such as CSS and client-side script: optional technology should complement the information on the site and its use, and should not interfere with access to it if this technology is not supported.

Guideline R-pd.1.3

Lost functionality

Lack of support for a technology can mean that certain functionality on a page is lost. For example: a drop-down menu will not drop down if client-side scripts are not supported. However, this does not have to mean that the visitor gets stuck, because an optional technology should complement the basic functionality on a page. For example, the drop-down menu could provide the option (by means of the label) of accessing a page where the visitor finds an expanded menu or another list of links. See also Progressive enhancement of functionality.

There are exceptions

Certain applications on a website do require support for an optional technology. Web developers are expected to be able to recognise these applications themselves. Two examples are described below.

  • Besides the regular content, a website provides a selection of information that is geared to the visitor’s preferences.
    Support for cookies may be necessary tp identify visitors. Without this support, selection will be missing. However, the regular content should remain accessible; for example, this content can provide an explanation about the need for cookie support to aid the unfortunate visitor.
  • Certain images, for instance maps or graphs, are sometimes difficult or impossible to describe by means of a text layer.
    In that case browser support for reproducing images is a prerequisite, and a visual impairment constitutes an obstruction. More information on this tricky situation is available in: Images and alternate text .


Web Guidelines version 1.3, November 2007.