True or False: 1.4.10 Reflow - Mobile and 320px testing

[A11yTea]

Hi everyone, I am requesting a clear answer to the following questions:

• Is mobile testing required for 1.4.10 Reflow? Or is mobile testing possible only if 320 CSS pixels (for vertical scrolling content) can be achieved with the phone? Like, let's say I have a phone with 430 CSS pixels of width. I assume that testing with that phone at 430 CSS pixels is not a legitimate test for this criteria.
• If content fails at 321 CSS pixels of width but passes at exactly 320 CSS pixels of width, then can I assume that it passes for Reflow? So Reflow does not care about any other widths but 320 CSS pixels (assuming vertical scrolling content), is that right?

[patrickhlauke]

Is mobile testing required for 1.4.10 Reflow

1,4,10 requires that you test at the specified viewport width or height. whether you do it on a phone, tablet, desktop browser, or something else is up to you.

If content fails at 321 CSS pixels of width but passes at exactly 320 CSS pixels of width, then can I assume that it passes for Reflow?

as written, the SC only applies for those exact widths/heights. nothing more.

[A11yTea]

I agree with you Patrick! I was posting because I am having a debate with someone. Thank you Patrick!

[TestPartners]

Given that the explicitly stated purpose of the SC is to allow users to enlarge the text without needing to scroll in two directions, it does not make any sense to do the test at 100% zoom on a small device. As has been discussed many times, this may well be 320 CSS pixels, but it's not the same as testing with a 1280px window at 400% zoom because floating elements obscure a much larger proportion of the screen in the latter case.

[grifare]

Why using 320px, both as a value and as one single threshold for testing, should be contested

For this criterion to be satisfied, even if WCAG currently seems to require that all content remains reachable on screens with exactly 320px width, I will keep believing that this WCAG directive does not make sense, for these reasons:

• 320px was too archaic even in 2018. It became unrealistically small to be adopted as a testing standard in 2025. In fact, the only method of testing is using emulation now, as no such devices exist. (I once bought a 1024px monitor from Value Village for 5 dollars to view it at 400% just as an easy solution.)
• More importantly, what if the website layout fails on many other screen sizes, but passes on some others including the magical number 320? Not common, but this is technically possible due to making CSS errors under media queries during development. I created an example to demonstrate just that.
• I would also consider introducing some sort of "being exempted" right clause for the website owners to this criterion. Some complex apps are simply not intended for cell phones. The app manufacturer can make a declaration such as "the minimum recommended screen size for this app is 1360px" and then that product should be tested against 1.4.10 at and after that threshold only.
  (For example, an architecture team is not supposed to design a skyscraper by AutoCAD, using their old cell phones while in metro.)

Here is my contribution to the Reflow discussion. Please test it.
https://www.grifare.net/examples/reflow/reflow.html

[patrickhlauke]

In fact, the only method of testing is using emulation now, as no such devices exist.

nobody says it must be tested on a device that has those metric. it is perfectly feasible to create a 320 css px wide viewport / 256 css px high viewport without "emulation" or anything else.

[grifare]

Thanks Patrick.
Terribly sorry, I just realised my link was broken! Could you please check it again and test how it looks on different sizes of screens, including 320px width?

[mraccess77]

It is my understanding that this criterion is not about mobile devices. It's about reading on any device - including a desktop/laptop. The requirement in my opinion is also not about about forcing the UI to fit in 320CSS pixels but about the length of blocks of content for reading that fit into that width (or height for vertical text).

[electrickite]

This question has come up for our team in the context of testing native mobile applications, or web applications that are only scoped to mobile user agents. As written, it does not seem possible to satisfy 1.4.10, simply because current devices do not support an effective resolution of 320px screen width and have no way to adjust the viewport width independent of the screen resolution. WCAG2ICT (which is, of course, non-normative) has this to say:

As written, this success criterion can only be met by non-web documents or software where the underlying user agent or platform can present content at a width equivalent to 320 CSS pixels for vertical scrolling content and a height equivalent to 256 CSS pixels for horizontal scrolling content.

When the underlying user agent or platform does not support these dimensions for scrolling, reflow is encouraged as this capability is important to people with low vision. As a reasonable benchmark, evaluate at the nearest size to what the Reflow success criterion specifies.

When users modify zoom, scaling, and/or display resolution at the platform software level (e.g. Operating System), it impacts the size of all applications and the platform software itself. This can result in improved readability in some applications but unwanted consequences in others.

Does this imply that native mobile applications, or mobile-specific web applications, for current gen devices cannot be said to conform with WCAG 2.1 or 2.2?

[pbossley]

We are also considering how testing can even be accomplished in the case of native mobile applications.