WCAG 2.x Priority levels discussion
Moved here from the WCAG 2.2 Success criterion acceptance requirements page. The purpose of this page is to facilitate review of the levels assigned to Success Criteria in WCAG 2.0 and 2.1, so as to inform the level assigned to new Success Criteria.
Background
The first iteration of this table was posted on 27 March 2017 and there was some discussion over the next few days on the wai-gl list. (One way to review that discussion is to view the archive by thread and look for the email message subject line “definition of the a/aa/aaa levels”. There are a total of fifteen messages in that thread.)
The table and the Further Discussion and Observations statements from WCAG 2.1 Success Criteria were the subject of a survey to working group members in April 2019.
Authoritative Reference
From Understanding Levels of Conformance (emphasis as in the original):
The Success Criteria were assigned to one of the three levels of conformance by the working group after taking into consideration a wide range of interacting issues. Some of the common factors evaluated when setting the level included:
- whether the Success Criterion is essential (in other words, if the Success Criterion isn't met, then even assistive technology can’t make content accessible)
- whether it is possible to satisfy the Success Criterion for all Web sites and types of content that the Success Criteria would apply to (e.g., different topics, types of content, types of Web technology)
- whether the Success Criterion requires skills that could reasonably be achieved by the content creators (that is, the knowledge and skill to meet the Success Criteria could be acquired in a week’s training or less)
- whether the Success Criterion would impose limits on the “look & feel” and/or function of the Web page. (limits on function, presentation, freedom of expression, design or aesthetic that the Success Criteria might place on authors)
- whether there are no workarounds if the Success Criterion is not met
Considerations for Tabulation
It is not possible to discriminate between ‘essential’ (first bullet) and ‘no workarounds’ (fifth and last bullet). In the tables that follow, these two factors have been combined into the “Essential” column.
The second factor, ‘all Web sites and types of content’ is reflected in the “All Content” column of the tables that follow.
The difficulty factor (i.e., ‘level of effort’) of the third bullet (reasonably be achieved by the content creators) is reflected in the tables that follow as the SC being “Easy” (or not). There are not any SC that require 40 hours of training, so there is a bit of hyperbole in that line from Understanding. Some SC are not technically challenging, but are labor intensive. (An example being 1.2.8 Media Alternative (Prerecorded), which is Level AAA.)
The ‘look and feel’ factor described in the fourth bullet is paraphrased in the tables that follow as the SC being “Invisible” — since the SC may be satisfied with no visual effect or with only trivial impact to the default presentation.
In the tables that follow, SC that are new to WCAG 2.1† are appended with the dagger symbol and highlighted in yellow.
Tabular View of Common Factors
Level A SC (n=30)
| SC# | SC Title | Essential | Easy | Invisible | All Content | Comment |
|---|---|---|---|---|---|---|
| 1.1.1 | Non-text Content | YES | YES | YES | YES | Easy, except for “alternative forms of CAPTCHA…” |
| 1.2.1 | Audio-only and Video-only (Prerecorded) | YES | no | no | YES | Not characterized as Easy since alternative formats are relatively labor intensive. |
| 1.2.2 | Captions (Prerecorded) | YES | no | no | YES | |
| 1.2.3 | Audio Description or Media Alternative (Prerecorded) | YES | no | no | YES | |
| 1.3.1 | Info and Relationships | YES | no | YES | YES | Many techniques associated with 1.3.1 are Easy, but this is an expansive SC, so it is not characterized as Easy. |
| 1.3.2 | Meaningful Sequence | YES | YES | YES | YES | |
| 1.3.3 | Sensory Characteristics | YES | YES | YES | YES | |
| 1.4.1 | Use of Color | YES | YES | no | YES | |
| 1.4.2 | Audio Control | YES | YES | no | YES | |
| 2.1.1 | Keyboard | YES | YES | YES | YES | Easy since standard HTML controls already meet this success criterion when used according to specification. This requirement was not even in WCAG 1.0. |
| 2.1.2 | No Keyboard Trap | YES | YES | YES | YES | As with 2.1.1, this was not even in WCAG 1.0. |
| 2.1.4† | Character Key Shortcuts | no | YES | YES | YES | |
| 2.2.1 | Timing Adjustable | YES | YES | no | YES | Characterized as Easy because the SC provides multiple good options. |
| 2.2.2 | Pause, Stop, Hide | YES | YES | no | YES | Characterized as Easy because the SC provides multiple good options. |
| 2.3.1 | Three Flashes or Below Threshold | YES | YES | no | YES | |
| 2.4.1 | Bypass Blocks | no | YES | no | YES | |
| 2.4.2 | Page Titled | no | YES | YES | YES | |
| 2.4.3 | Focus Order | no | YES | YES | YES | |
| 2.4.4 | Link Purpose (In Context) | no | YES | YES | YES | |
| 2.5.1† | Pointer Gestures | YES | no | no | YES | |
| 2.5.2† | Pointer Cancellation | YES | YES | YES | YES | |
| 2.5.3† | Label in Name | YES | YES | YES | YES | |
| 2.5.4† | Motion Actuation | YES | YES | YES | YES | |
| 3.1.1 | Language of Page | no | YES | YES | YES | |
| 3.2.1 | On Focus | YES | YES | YES | YES | |
| 3.2.2 | On Input | YES | YES | no | YES | Not characterized as Invisible because it frequently requires adding an explicit submit button (which otherwise might not have been in the original design). |
| 3.3.1 | Error Identification | YES | YES | YES | YES | Characterized as Easy and Invisible because this SC presumes that the page is already designed to convey error messages to the user. |
| 3.3.2 | Labels or Instructions | YES | YES | no | YES | |
| 4.1.1 | Parsing | YES | no | YES | YES | |
| 4.1.2 | Name, Role, Value | YES | no | YES | YES | This can be Easy, since (per the Note) “standard HTML controls already meet this success criterion when used according to specification.” Not characterized as Easy because it does require some care when using ARIA, for almost all scripting, and does limit use of 3rd party libraries. Also per the Note: “This success criterion is primarily for Web authors who develop or script their own user interface components.” |
Level AA SC (n=20)
| SC# | SC Title | Essential | Easy | Invisible | All Content | Comment |
|---|---|---|---|---|---|---|
| 1.2.4 | Captions (Live) | YES | no | no | YES | |
| 1.2.5 | Audio Description (Prerecorded) | YES | no | no | YES | |
| 1.3.4† | Orientation | YES | YES | YES | YES | Characterized as Easy and Invisible since the feature is enabled by default. |
| 1.3.5† | Identify Input Purpose | no | no | YES | YES | |
| 1.4.3 | Contrast (Minimum) | no | YES | no | YES | Not characterized as Essential because AT provides explicit features for enhancement of text. |
| 1.4.4 | Resize text | no | YES | YES | YES | In 2008, before widespread browser zoom, this was neither Easy nor Invisible. |
| 1.4.5 | Images of Text | no | no | YES | YES | |
| 1.4.10† | Reflow | YES | no | no | YES | Characterized as All Content because SC has a significant exception. |
| 1.4.11† | Non-Text Contrast | YES | no | no | YES | Characterized as Essential because AT is not as good at enhancement of non-text content (as compared to the options for enhancing text). |
| 1.4.12† | Text Spacing | no | YES | no | YES | Not characterized as Essential because AT provides explicit features for enhancement of text. |
| 1.4.13† | Content on Hover or Focus | YES | no | no | YES | Exception for Title element makes this SC easier, but it still requires care to implement. |
| 2.4.5 | Multiple Ways | no | no | no | YES | |
| 2.4.6 | Headings and Labels | no | YES | no | YES | |
| 2.4.7 | Focus Visible | YES | YES | no | YES | |
| 3.1.2 | Language of Parts | no | no | YES | YES | |
| 3.2.3 | Consistent Navigation | no | YES | YES | YES | |
| 3.2.4 | Consistent Identification | no | YES | YES | YES | |
| 3.3.3 | Error Suggestion | no | no | no | YES | |
| 3.3.4 | Error Prevention (Legal, Financial, Data) | no | no | no | YES | |
| 4.1.3† | Status Messages | no | YES | YES | YES |
Level AAA SC (n=28)
| SC# | SC Title | Essential | Easy | Invisible | All Content | Comment |
|---|---|---|---|---|---|---|
| 1.2.6 | Sign Language (Prerecorded) | no | no | no | no | |
| 1.2.7 | Extended Audio Description (Prerecorded) | no | no | no | no | |
| 1.2.8 | Media Alternative (Prerecorded) | no | no | no | YES | |
| 1.2.9 | Audio-only (Live) | YES | no | no | no | |
| 1.3.6† | Identify Purpose | YES | no | no | YES | Characterized as All Content since SC is explicitly scoped to be limited markup languages only. |
| 1.4.6 | Contrast (Enhanced) | no | YES | no | YES | |
| 1.4.7 | Low or No Background Audio | YES | no | no | no | |
| 1.4.8 | Visual Presentation | YES | no | no | no | |
| 1.4.9 | Images of Text (No Exception) | no | no | no | no | |
| 2.1.3 | Keyboard (No Exception) | YES | no | no | no | |
| 2.2.3 | No Timing | YES | no | no | no | |
| 2.2.4 | Interruptions | YES | no | no | no | |
| 2.2.5 | Re-authenticating | YES | no | no | no | |
| 2.2.6† | Timeouts | no | no | YES | no | |
| 2.3.2 | Three Flashes | YES | no | no | no | |
| 2.3.3† | Animation from Interactions | YES | YES | no | no | |
| 2.4.8 | Location | no | no | no | no | |
| 2.4.9 | Link Purpose (Link Only) | no | YES | no | no | |
| 2.4.10 | Section Headings | no | YES | no | no | |
| 2.5.5† | Target Size | no | YES | no | no | |
| 2.5.6† | Concurrent Input Mechanisms | no | YES | YES | YES | |
| 3.1.3 | Unusual Words | no | no | no | no | |
| 3.1.4 | Abbreviations | no | YES | no | no | |
| 3.1.5 | Reading Level | YES | no | no | no | |
| 3.1.6 | Pronunciation | no | no | no | no | |
| 3.2.5 | Change on Request | YES | no | no | no | |
| 3.3.5 | Help | no | no | no | no | |
| 3.3.6 | Error Prevention (All) | no | no | no | YES |
Tally by Levels
| Essential | Easy | Invisible | Essential and (either Easy or Invisible) |
Both Easy and Invisible | All Content | |
|---|---|---|---|---|---|---|
| A (25) | 19 (76%) | 19 (76%) | 15 (60%) | 17 (68%) | 11 (44%) | 25 (100%) |
| AA (13) | 2 (15%) | 6 (46%) | 6 (46%) | 0 (0%) | 4 (31%) | 13 (100%) |
| AAA (23) | 10 (43%) | 4 (17%) | 0 (0%) | 0 (0%) | 0 (0%) | 3 (13%) |
Observations
Representative examples of ‘essential’ in WCAG 2.0 are: 1.1.1 Non-text Content, 1.2.2 Captions (Prerecorded), and 2.1.1 Keyboard. The workarounds (e.g., file name, automatic captions, mouse keys) are very inadequate.
Four SC are ‘blocking’, which is to say they are reference by Conformance Requirement 5 for Non-Interference: 1.4.2 - Audio Control, 2.1.2 - No Keyboard Trap, 2.3.1 - Three Flashes or Below Threshold, and 2.2.2 - Pause, Stop, Hide. These SC are all at Level A.
There are only five (out of 25) 2.0 Level A SC that are not Essential. Of these five, four are both Easy and Invisible.
2.4.1 Bypass Block 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).
The ‘All Content’ consideration is the major discriminating factor for AAA. All A and AA SC are applicable to all Web sites and types of content. It is only AAA SC that might not satisfy the ‘all content’ consideration.
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 2.0 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).