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Progressive enhancement and accessibility redux

A while ago I asked about the exact relationship between progressive enhancement and accessiblity. What were the responses?

The resulting Twitter thread was interesting, and basically boiled down to this:

Progressive enhancement is an important accessibility tool.

I can agree with that without reservation, but still had a nagging feeling that this was not the entire story.

Then I received a private communication from Josh Fremer that connected the dots for me. His mail is worth quoting at length — with permission:

I think of [progressive enhancement and accessibility] as the same process, but with different foci. Accessibility aims to optimize an experience across a spectrum of user capabilities. Progressive enhancement aims to optimize an experience across a spectrum of user _agent_ capabilities.

Indeed, if you broaden the definition of "user agent" to include a user's physiology, I think the concepts become nearly identical.

What is the application of color to a website if not a progressive enhancement targeting user agents that can discern colors? Whether the "agent" in this case is the electronic device in the user's hands or the cells in their eyes is kind of moot. The principles of both PE and accessibility require us to consider the user who is unable to receive color information.

Conversely, what is the inability to process javascript other than a "disability" of the user agent? We would probably call handling this case a PE concern, but what If the user has disabled javascript in order to mitigate a physical disability? The capabilities of the user agent have been modified to better match the capabilities of the user and now it starts to look like an accessibility issue.

In closing a fun little thought experiment is to imagine a sci fi future in which users can plug computers directly into their brains, or swap their personalities into different bodies with different capabilities. This further blurs the line between what we traditionally call a "user agent" and a user's innate disabilities. "This web site is best viewed in a body with 20/20 vision and quick reflexes."

Food for thought.

(Josh promised to write an article about his idea, which I’ve never seen expressed like this before. If you have seen a similar argument, please let me know. Once Josh’s article is live I’ll include a link in this post.)