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Success Criterion 2.5.8: Target Size (Minimum) (Level AA) #80
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@pday1 I unfortunately don’t have any experience with an alternative to pixels, either. |
Just jumping in, in relation to that "note 1", to say: while yes, there is an ideal definition for what size a reference pixel would be, the reality will depend on many more factors, not least of them decisions taken by device manufacturers. there is no guarantee that in the wild, a relationship such as "6.24mm can be taken as an approximate equivalent for 24 CSS pixels" will be true, and it's outside of a developer's control to know/address this for the most part. the same holds true for operating-system-specific measurements, such as Apple's "points" - which are different from typographic points. overall there's basically very little guarantee (except when working specifically on a known device) that an author can accurately predict the real-world (as measured on screen) dimensions of something they define. which is why for WCAG, we had to settle for CSS pixels (which are also the base unit of measure that all other units in CSS, like |
Please note that the "inline" exception has been refined as part of the work with moving WCAG 2.2 to CR.
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@pday1 Is this ready for the Task Force to review? |
@maryjom I think it could be useful to discuss next week - at least to get more input from the wider team. |
Along with the discussion of the SC interpretation itself are the new definitions that come with this SC: CSS pixelFrom the WCAG 2.2 definition for CSS pixel:
pointer input
targetFrom the WCAG 2.2 definition for target:
This applies directly as written and as described in the WCAG 2.2 glossary, replacing “Web page” with “non-web document or software”. With this substitution, it would read: target
target offsetFrom the WCAG 2.2 definition for target offset:
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@pday1 This is an SC that WCAG 2.2 moved from a Level AAA to Level AA requirement. Along with that, it appears there are a number of changes to the language of 2.5.8 Target Size (Minimum) in WCAG 2.2 as part of that movement. The project labels this SC to be part of WCAG 2.2 incorporations into the WCAG2ICT Note, so I would prefer to work on issues labeled with WCAG 2.1 for now. Apologies for not noticing that earlier. |
OK no problem. I suggest we park this then - I've put a note in the title |
As an aside... When we talk about 2.5.8 touch target, info I found about fingertip size:
The U.S. govt. website is recommending touch targets be 44px by 44px. I'm not sure if they mean CSS pixels or actual pixels - it isn't clear. Also, I found this Android Developers' video on touch target testing (from 1 year ago) that supports use of the platform-specific density-independent pixels (DP) when testing the touch target size. The test tool he used in the video was checking for 48 x 48 DP. Not sure how that compares in size to the 24 x 24 CSS pixels required by 2.5.8 touch target or if this is instead testing for the AAA which is 44 x 44 CSS pixels. Nielsen Norman Group has an article on Touch Targets on Touchscreens where the conclusion says to have usable touch targets, they should measure at least 1 cm x 1 cm in the rendered size with adequate space (unspecified in the article) between touch targets. |
again: unless they are designing for one, unchangeable, known physical screen size at a known, unchangeable resolution, authors cannot control the real-world (as measured on the physical screen) size that content/controls are rendered. which is why even apple, google, and microsoft guidance uses abstracted measures like dp, point, effective pixel - rather than cm.
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@patrickhlauke I understand, but we also have to interpret for software on closed products - where the CSS pixel size and device-independent pixels may have no meaning whatsoever. So the SC, as it is written, is not so easily applied. Usability information gleaned from these, and potentially other sources, would have to inform some other form of requirement or best practice. |
sure, but my point is a measure of size that relates to actual physical size as measured on the device/screen will for non-web documents will turn this into direct conflict with web documents which do not (and cannot) base things on actual physical size. so potentially on the same device you'd start having things that pass if they're web content but fail if they happen to be non-web/native, or vice-versa. |
(note that this discussion here is target size, not reflow capability) |
My former comment deleted. I had reflow on the brain because of this morning's WCAG2ICT meeting. |
@pday1 In the 2nd half of the 25 May meeting, we decided to see if this SC would be easier to think about with regard to CSS pixels and application to non-web software and documentation. Can you make the necessary updates to include the latest language for 2.5.8 Target Size from the WCAG 2.2 Candidate Recommendation published recently? We'd like to discuss this in the 1 June meeting. |
(Taking latest CR language and combining with discussion on CSS pixels ...) From Success Criterion 2.5.8:
Additional Guidance When Applying Success Criterion 2.5.8 to Non-Web Documents and Software: This applies directly as written, and as described in Intent from Understanding Success Criterion 2.5.8 and Benefits from Understanding Success Criterion 2.5.8 (also provided below).
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I was pondering whether software platforms with very small, very large, or distant screens might cause anything in this criterion to become problematic. My conclusion: There's no problem. I considered the following examples.
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@patrickhlauke wrote
If a platform has a web browser on it, then it's possible to measure native software dimensions in terms of CSS pixels.
Is there any software platform where this doesn't work? I can't think of any. |
In my last two comments, I've been careful to say "software" platforms. PDF is problematic for SC 2.5.8 Target Size. So I'm thinking of a note something like the following. It's probably more general than just for Target Size.
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Are there other notes needed for documents? I see @mitchellevan proposed:
However, is the "intended usage" of the content always known, and would the "appropriate zoom level" be obvious? |
Changes agreed in WCAG2ICT call on 1st June.
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I've taken comments and agreed upon changes from the meeting and synthesized into the following: From Success Criterion 2.5.8:
Additional Guidance When Applying Success Criterion 2.5.8 to Non-Web Documents and Software:This applies directly as written, and as described in Intent from Understanding Success Criterion 2.5.8 (also provided below), replacing "user agent" with "user agent or platform software". With these substitutions, it would read:
(for non-web documents) Note: Some document formats do not have a default zoom level, but have commonly available user agents that allow users to view the content at a wide range of sizes. When evaluating such documents, it is a best practice to choose a starting zoom level appropriate for the intended usage of the content. (for non-web software) NOTE 1: Non-web software and their accompanying platform software do not use measurements of CSS pixels. Therefore, platform-specific pixel density-independent measurements should be used. Examples include: px in iOS and MacOS, density-independent pixels (DP) for Android, and device-independent pixels for Windows. NOTE 2: Non-web software that either doesn't have the concept of device or density independent pixels or measurements by pixels, should use the formula contained in the definition of a reference pixel to calculate the arc-length of the viewing angle using the optimal viewing distance from the screen to calculate the reference pixel size.
As an example, for a system that is designed to be read at approximately an arm's length, 6.24mm can be taken as an approximate equivalent for 24 CSS pixels, as at that distance, 1px corresponds to about 0.26 mm (1/96 inch). NOTE 3: See also the discussion on Closed Functionality. The specific content to add to the Appendix on SC problematic for closed functionality is being developed by the sub-group. Definitions to add for this SC:To the section Glossary Items that Apply to All Technologies, add:
To the section Glossary Items with Specific Guidance, add: target NOTE Guidance When Applying “target” to Non-Web Documents and SoftwareThis applies directly as written and as described in the WCAG 2.2 glossary, replacing “page” with “non-web document or content presented by software”. With this substitution, it would read: NOTE |
Note the nitpicks/extra thoughts on this over on #162 (comment) |
After the 8 June conversation, this is where we landed: From Success Criterion 2.5.8:
Additional Guidance When Applying Success Criterion 2.5.8 to Non-Web Documents and Software:This applies directly as written, and as described in Intent from Understanding Success Criterion 2.5.8 (also provided below), replacing "user agent" with "user agent or platform software", and "on the same page" with "in the same non-web document or software". With these substitutions, it would read:
(for non-web documents) Note: Some document formats do not have a default zoom level, but have commonly available user agents that allow users to view the content at a wide range of sizes. When evaluating such documents, it is a best practice to choose a starting zoom level appropriate for the intended usage of the content. (for non-web software) NOTE: See also the discussion on Closed Functionality. The specific content to be added to the Appendix on SC problematic for closed functionality is being developed by the sub-group. Definitions to add for this SC:To the section Glossary Items that Apply to All Technologies, add:
To the section Glossary Items with Specific Guidance, add: target NOTE Guidance When Applying “target” to Non-Web Documents and SoftwareThis applies directly as written and as described in the WCAG 2.2 glossary, replacing “page” with “non-web document or content presented by software”. With this substitution, it would read: NOTE Notes for the CSS definition@ferBonnin is investigating what terms are used in Microsoft products. Patrick mentioned "effective pixels" (epx), but I had based the proposal on what I had found - a fairly recent [Windows App Development article](DirectWrite measures font sizes in DIPs) on the Microsoft site comparing DIP and "device independent pixels" and says that DeviceWrite uses DIP. Maybe for Win32 apps DIP is used and then EPX is used for Universal Windows Platform apps?
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Adding target as definition term per #80 (comment)
From our 2023-06-01 Task Force discussion on target size I offered to try to update this part of the draft:
The idea was: could evaluating a PDF for 2.5.8 Target Size be based on the "actual size" viewing of the PDF? A limitation is that not all PDF viewers (a.k.a. user agents) give the user a way to view the PDF at actual size. I tried viewing a downloaded Yosemite Park map PDF in the following user agents:
The PDF viewing user agents on Windows offered an easy to find "100%" or "actual size" zoom level, but the mobile user agents neither defaulted to "actual size" nor offered a way to switch to it. These mobile user agents neither inform the user of the current zoom level nor offer a choice of discrete zoom levels; they only offer a wide continuous range of zoom. Another problem with relying on "actual size" comes from the fact that it is a print concept. Suppose a PDF contained links designed for usable target sizes in a desktop user agents, yet the "actual size" was set in the PDF for a tiny piece of paper such as a 55 mm wide business card. This would cause the 2.5.8 evaluation to fail for a reason that doesn't actually affect users. So I suggest we do one of two things.
Acrobat Viewer on Android, just after opening a downloaded PDF of a wide mapAcrobat Viewer on Windows: the same PDF with zoom set to "actual size" |
On 29 June, the TF agreed to update the non-web documents note as follows: (for non-web documents) |
I think I had missed this one in the closed functionality survey because 2.5.8 is actually a WCAG 2.2 criteria and we hadn't really discussed those further in our sub-group meetings. So if we don't have this bullet ready for the First Public Working Draft, we can just add an editor's note on the 2.5.8 SC guidance that it will be developed for the next draft. |
Notes 1 and 2 need rework. This is a very rough note as a reminder to myself, rather than being a well-written proposal, suitable for review! |
Copying in the thoughts from the Google spreadsheet Closed Functionality analysis of the SC:
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@pday1 Once you get the closed functionality bullets to a state where the TF can review them, I can add them to the next survey. |
The word 'page' is web specific and not applicable to non-web ICT. |
Re: Sam's comment - While page should be removed, we need to find a way to make sure the alternative isn't just available anywhere in the software but within the same context as otherwise this could be met in unintended ways that do not provided an equitable experience. |
Sorry. @maryjom resolved issue in her comment #80 (comment) with replacing "on the same page" with "in the same non-web document or software". |
Since this SC has been incorporated into the WCAG2ICT FPWD, I've spun off remaining work into a new issue - #258. This way we'll have a fairly clean comment stream. |
From Success Criterion 2.5.8:
Additional Guidance When Applying Success Criterion 2.5.8 to Non-Web Documents and Software:
This applies directly as written, and as described in Intent from Understanding Success Criterion 2.5.8 and Benefits from Understanding Success Criterion 2.5.8 (also provided below).
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