100% accessible is impossible, but that’s okay. It can still be a good thing to aim for, to use as a direction.
What does 100% accessible even mean?
100% of what? 100% of the WCAG Success Criteria passed? 100% of a checklist completed? 100% score on a user survey?
Accessibility isn’t one specific thing. We can’t point at it at directly.
When do we measure it?
Many web-based products update frequently. Particularly fast ones update a few times a day. But even the slower ones usually have content that updates quickly.
Any measurement of a product’s accessibility can only be a snapshot in time. This can be a good thing. A series of snapshots over time can give us a feeling for how we’re doing over time. But accessibility isn’t a “one-and-done” thing. It’s an ongoing commitment to quality and usability.
Where do we measure it?
Many web apps are… complex. They have a lot of pages, and a lot of states. Even just making a list of pages and states to test can be a complex endeavour. To then test all those can be an epic quest.
Who is it 100% accessible for?
Humans beings have a very wide range of abilities and capabilities. We use a wide variety of technology. What works for some humans might not work for some others.
How do we measure it?
After a bit of set-up, automated tests are quick and easy to run. But they can only catch some errors. They’re much more geared towards quantitative measuring than qualitative measuring. They can answer “Does this field have a label?”. But they can’t answer “Does this field have a good (meaningful, clear, useful) label?”
So we need to do some manual testing ourselves, some testing with our users (ideally with a wide range of them). That means more time and effort.
So now what?
Even if we can’t say what “100% accessible” is, and we certainly can’t reach it, that doesn’t mean it’s not a useful idea or target. Maybe the best thing to do is focus on improvement.
The W3C’s Developing an Accessibility Statement I think points in a good direction. A statement of intent, and a list of what we’re doing to support that.
We’re committed to ensuring digital accessibility for people with disabilities. We are continually improving the user experience for everyone, and applying the relevant accessibility standards.
An Accessibility Statement can also list: Measures to support accessibility, Evaluation Methods Used, and (importantly) Limitations and alternatives.
The last one is important because it acknowledges a perhaps slightly awkward truth: we’ve still got work to do. Nothing can be “100% accessible”. But we can aim at it, and get better with every iteration.