RE: definition of the a/aa/aaa levels

Regarding the 5 level A criteria you determined didn't meet the logic:

1. 1.2.*: CC, AD, and transcripts are nearly always invisible, no?

2. 1.3.1: Yes, this can be a big and complex criterion, but in most cases it's not hard to meet the essential pieces and nearly all of the techniques are invisible.

3. 2.4.1: I would certainly disagree with being able to programmatically bypass repeated blocks of content as not being essential for navigation, and again this is nearly always invisible.


-----Original Message-----
From: Bailey, Bruce [] 
Sent: Monday, March 27, 2017 8:53 AM
To: WCAG <>
Cc: Andrew Kirkpatrick <>; Joshue O Connor ( <>
Subject: definition of the a/aa/aaa levels 

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).




Received on Wednesday, 29 March 2017 21:26:50 UTC