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Computing and Information Services

Accessibility and Search Engines

Search engines play an important role in the web, and a site that is accessible to them will clearly be ranked more highly. Search engines support a limited sub-set of HTML, which means that a site must be viewable using only that sub-set.

Fortunately, the majority of HTML will degrade gracefully and so no special work is required. However:

  • Frames are supported by very few search engines
  • Javascript is supported by very few (if any) search engines
  • Java and Flash are supported by no search engines (while some are working on partial support for Flash, this is unlikely to be of a high standard)
  • Documents not in HTML format, such as Microsoft word documents and PDF files are supported by some search engines, but may not be treated in the same way as HTML files when constructing the search engine's "map" of the site.

If the site has been designed in an accessible manner, however, there will be accessible alternatives that search engines can use to index the pages. Otherwise, not only will some users be unable to access information on the site, but it will be unlikely to be indexed properly by search engines.

One of the recommendations for accessible site design is that the site be written using structural markup instead of presentational markup. As well as accessibility advantages, this also improves the ability of modern search engines to index the page correctly.

This Search Engine Simulator can demonstrate why accessibility to search engines is important. Try looking at a mix of sites with it. Especially look at sites that use frames as most, sadly, do not provide accessible alternatives.