RE: definition of the a/aa/aaa levels

Thanks for the feedback Greg.  I regret using the word “definition” to characterize the action assignment.  Please excuse the confusion.

I agree and understand completely that there are no absolute rules or clear algorithms for deciding between A / AA / AAA.

I agree and understand that what the Understanding currently says is pretty much all that can be said with any kind of certainty and working group consensus.

I especially want to echo your concluding remark:
> We could find no concrete formula to describe their placement and when we tried to use a formula - some ended up in the wrong levels.

That all said, I think my sorting helps reveal some after-the-fact patterns:

Those are patterns, not hard and fast rules.

I do not think it is at all controversial to say that our work on level assignments for 2.1 can and should be informed by the 2.0  level assignments.

-----Original Message-----
From: Gregg C Vanderheiden [] 
Sent: Monday, March 27, 2017 9:46 AM
To: Bailey, Bruce <>
Cc: w3c-waI-gl@w3. org <>; Andrew Kirkpatrick <>; Joshue O Connor <>
Subject: Re: definition of the a/aa/aaa levels

Thanks Bruce

As you can see — the levels cannot be defined by those factors (or any factors clearly).  They are some of the factors but not all - and even these do not account for the levels of the SC.

We tried to do this in the WCAG 2.0 working group too.  

The WCAG 2.0 working group that assigned the SC to the levels worked hard to describe the levels — but there was so much involved in the decisions - including the interaction of each SC with the other SC at that or another level — that the language used in the Understanding WCAG 2.0 is the only language that is accurate in describing the way levels were defined.

there are simply 3 levels

A  = Minimum needed for any conformance.
AA =  Better 
AAA = and Better still   (Noting that some AAA cannot be applied everywhere so level AAA should not be required) 

Even AAA does not make web pages accessible.  (Even all of the advisory techniques do not) 

So we can’t define the levels as meaning anything specific.   They are just 3 levels of conformance with no absolute meaning outside of the Guidelines. 

And the only thing that can be said for sure about why an SC is at any level is that, after considering the factors listed (in Understanding WCAG 2.0 ) the level of the SC was the level that the working group could reach consensus on for that SC. 

WCAG 2.0 was a total consensus document.    All SC wording and levels had the unanimous agreement of the Working Group.   (NOTE: Consensus does not mean that that is where everyone wanted everything.  It means that, in the end, the SC were worded and placed in a way that  everyone could live with them. 

So what is in Understanding WCAG 2.0 is the best that could.can be said about the factors that the WG used to place the SC.  We could find no concrete formula to describe their placement and when we tried to use a formula - some ended up in the wrong levels.



Gregg C Vanderheiden

> On Mar 27, 2017, at 8:53 AM, Bailey, Bruce <> wrote:
> On the March 21st call, I took the action item to work on the definition between levels.  This work is posted on the wiki [1] and summarized in this email.
> Based on [2] Understanding Levels of Conformance, I boiled the factors discussed there down to four characterizations:
> Essential:  If the Success Criterion isn’t met, then even assistive technology can’t make content accessible; or there are no workarounds; or the content is blocking. 
> Easy:  The Success Criterion is not technically challenging to implement and requires only minimal effort. 
> Invisible:  The Success Criterion imposes only trivial limits on the “look & feel” and/or function of the Web page. 
> All Content:  It is possible to satisfy the Success Criterion for all Web sites and types of content.
> I then went through each WCAG 2.0 SC and made a yes/no determination 
> for each of those four characterizations. [3]
> There is obviously plenty of room for debate with the above two steps, but assuming it is all reasonably close, I offer the following observations:
> In general, WCAG 2.0 Level A SC are:  either [essential and (easy or invisible)] or [both easy and invisible].  20 of 25 Level A SC are characterized this way.
> There are five Level A SC that are exceptions to the above general rule for Level A.  They are:  1.2.1 Audio-only and Video-only (Prerecorded), 1.2.2 Captions (Prerecorded), 1.2.3 Audio Description or Media Alternative (Prerecorded), 1.3.1 Info and Relationships, and 2.4.1 Bypass Blocks.
> 2.4.1 Bypass Block is an outlier because it is the only WCAG 2.0 Level A SC that is not essential and not [both easy and invisible].
> In general, WCAG 2.0 Level AA SC are not essential.  Only 2 of 13 are essential, namely 1.2.4 Captions (Live), and 1.2.5 Audio Description (Prerecorded).
> In general, WCAG 2.0 Level AAA SC are not possible for all content.  21 of 24 Level AAA SC are characterized this way.
> There are three Level AAA SC that are exceptions to the above general rule for Level AAA.  They are:  1.2.8  Media Alternative, 1.4.6  Contrast (Enhanced), and 3.3.6  Error Prevention (All).
> [1] 
> [2] 
> [3] 

Received on Monday, 27 March 2017 14:12:04 UTC