An Overview of WCAG’s Fourth Principle: Robust

1 guideline. 3 success criteria (including 2 Level A conformance. 1 Level AA conformance). And a few ever-changing techniques that are sufficient, advisory, or a failure. As I pointed out in my Perceivable principle, Operable principle, and Understandable principle reviews, these stats are just one way the World Wide Web Consortium’s (W3C) “Robust” principle within the current Web Content Accessibility Guidelines (WCAG)  2.1 recommendation can be broken down.


On that note, I’ll introduce you to WCAG’s fourth and shortest principle: Robust. This short, and likely understated, principle boils down to creating flexible content and interfaces so that everyone can access your website now, and in the future, in ways and methods you can’t plan for. Technology gets updated, outdated, and revived quickly in the 21st century. We, as developers, can’t plan for everything, but we can make strides to be forward-thinking with our code.

The fourth Web Content Accessibility Guideline‘s says: “Content must be robust enough that it can be interpreted by by a wide variety of user agents, including assistive technologies.” This is a generally defined idea, leading up to more objective goals (success criteria) and techniques.

This principle offers us suggestions and insights to successfully make our websites flexible and more inclusive, inviting more people to interact with it in a way that maybe different than our own. “Robust” models a way for us to be considerate of people who think differently, move differently, and perceive differently than ourselves. No matter the physical and cognitive differences among us, everyone should still be able to use your website with very few hurdles.


To dig a little deeper, how can we ensure that everyone can understand the services and information we have to offer? Step down a level, from subjective to objective, via its guideline and success criteria. The one Robust guideline says that your entire webpage should be:

  • compatible

Success Criteria

Digging deeper, we find this guideline offers its own goals (success criteria) to target common accessibility problems. To sum up the 3 goals that the criteria are aiming for:

  • markup should be parsable (valid and complete)
  • a name, role, and value should be assigned (to custom elements)
  • status messages about changes or alerts should be announced, even without focus on that element

I encourage you to check out all the success criteria, now that you are more confident in understanding the guideline within the fourth principle. Additionally, read How to Meet WCAG, which is add value to your understanding and clear techniques that help you visualize how to meaningfully apply what you’ve learned.


Regardless of how you take your next steps, I hope you’re becoming more confident to dive into WCAG documentation and its supplemental materials and guides to help you better understand web accessibility. I can’t emphasize enough that, despite all the technical specs, taking a moment to empathize with people who have different levels of abilities than your own is so important. Ask yourself, “How could my website prevent a person with a visual, hearing, physical, or cognitive impairment from entering in and walking away with what they came for?” In the end, it’s the empathizing and relating to your wider audience that will make your accessibility efforts a success, rather than all the vast technical memorization and compliance, in which you devoted your time.

An aside

This is Day 10 of my 100 Days of Accessibility journey to learn all things web accessibility. The best way I retain information is to share with others, so I spent my “study” time today writing this post to advance my knowledge, and yours, too.

As an aside resource that I’m currently reading, Form Design Patterns by Adam Silver (Smashing Magazine) is reinforcing my assimilation of the Robust principle. I’ve only read through his first form pattern about registration forms, but it reinforces the importance of semantic markup. Clear markup benefits all users.

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