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1.4.6: Contrast (Enhanced): (AAA)

Note: To find more information on items such as G14: for example, visit the "Understanding"link at the bottom of each Guideline

The visual presentation of text and images of text has a contrast ratio of at least 7:1, except for the following: (Level AAA)

  • Large Text: Large-scale text and images of large-scale text have a contrast ratio of at least 4.5:1;
  • Incidental: Text or images of text that are part of an inactive user interface component, that are pure decoration, that are not visible to anyone, or that are part of a picture that contains significant other visual content, have no contrast requirement.
  • Logotypes: Text that is part of a logo or brand name has no minimum contrast requirement.

Sufficient Techniques for 1.4.6 – Contrast (Enhanced)

Situation A: text is less than 18 point if not bold and less than 14 point if bold

  • 1.G17: Ensuring that a contrast ratio of at least 7:1 exists between text (and images of text) and background behind the text
  • 2.G148: Not specifying background color, not specifying text color, and not using technology features that change those defaults
  • 3.G174: Providing a control with a sufficient contrast ratio that allows users to switch to a presentation that uses sufficient contrast

Situation B: text is as least 18 point if not bold and at least 14 point if bold

  • 1.G18: Ensuring that a contrast ratio of at least 4.5:1 exists between text (and images of text) and background behind the text
  • 2.G148: Not specifying background color, not specifying text color, and not using technology features that change those defaults
  • 3.G174: Providing a control with a sufficient contrast ratio that allows users to switch to a presentation that uses sufficient contrast

Advisory Techniques for 1.4.6 – Contrast (Enhanced)

  • G156: Using a technology that has commonly-available user agents that can change the foreground and background of blocks of text
  • Using a higher contrast value for text that is over a patterned background
  • Using Unicode text and style sheets instead of images of text
  • Using a higher contrast values for lines in diagrams
  • Using greater contrast level for red-black text/background combinations
  • Using colors that are composed predominantly of mid spectral components for the light and spectral extremes (blue and red wavelengths) for the dark
  • Using a light pastel background rather than a white background behind black text to create sufficient but not extreme contrast
  • Making icons using simple line drawings that meet the contrast provisions for text
  • Providing sufficient color contrast in graphs and charts
  • Using a 3:1 contrast ratio or higher as the default presentation
  • Providing sufficient color contrast for empty text fields

Failures for SC 1.4.6 – Contrast (Enhanced)

  • F24: Failure of Success Criterion 1.4.3, 1.4.6 and 1.4.8 due to specifying foreground colors without specifying background colors or vice versa
  • F83: Failure of Success Criterion 1.4.3 and 1.4.6 due to using background images that do not provide sufficient contrast with foreground text (or images of text)

http://www.w3.org/TR/UNDERSTANDING-WCAG20/visual-audio-contrast7.html

Conformance

See http://www.w3.org/TR/WCAG20/ for more detail.

This section lists requirements for conformance to WCAG 2.0. It also gives information about how to make conformance claims, which are optional. Finally, it describes what it means to be accessibility supported, since only accessibility-supported ways of using technologies can be relied upon for conformance.

Understanding Conformance includes further explanation of the accessibility-supported concept.

Conformance Requirements

In order for a Web page to conform to WCAG 2.0, all of the following conformance requirements must be satisfied:

1. Conformance Level:

One of the following levels of conformance is met in full.

  • Level A: For Level A conformance (the minimum level of conformance), the Web page satisfies all the Level A Success Criteria, or a conforming alternate version is provided.
  • Level AA: For Level AA conformance, the Web page satisfies all the Level A and Level AA Success Criteria, or a Level AA conforming alternate version is provided.
  • Level AAA: For Level AAA conformance, the Web page satisfies all the Level A, Level AA and Level AAA Success Criteria, or a Level AAA conforming alternate version is provided.

Note 1: Although conformance can only be achieved at the stated levels, authors are encouraged to report (in their claim) any progress toward meeting success criteria from all levels beyond the achieved level of conformance.

Note 2: It is not recommended that Level AAA conformance be required as a general policy for entire sites because it is not possible to satisfy all Level AAA Success Criteria for some content.

2. Full pages:

Conformance (and conformance level) is for full Web page(s) only, and cannot be achieved if part of a Web page is excluded.

Note 1: For the purpose of determining conformance, alternatives to part of a page's content are considered part of the page when the alternatives can be obtained directly from the page, e.g., a long description or an alternative presentation of a video.

Note 2: Authors of Web pages that cannot conform due to content outside of the author's control may consider a Statement of Partial Conformance.

3. Complete processes:

When a Web page is one of a series of Web pages presenting a process (i.e., a sequence of steps that need to be completed in order to accomplish an activity), all Web pages in the process conform at the specified level or better. (Conformance is not possible at a particular level if any page in the process does not conform at that level or better.)

Example: An online store has a series of pages that are used to select and purchase products. All pages in the series from start to finish (checkout) conform in order for any page that is part of the process to conform.

4. Only Accessibility-Supported Ways of Using Technologies:

Only accessibility-supported ways of using technologies are relied upon to satisfy the success criteria. Any information or functionality that is provided in a way that is not accessibility supported is also available in a way that is accessibility supported. (See Understanding accessibility support.)

5. Non-Interference:

If technologies are used in a way that is not accessibility supported, or if they are used in a non-conforming way, then they do not block the ability of users to access the rest of the page. In addition, the Web page as a whole continues to meet the conformance requirements under each of the following conditions:

  • 1.when any technology that is not relied upon is turned on in a user agent,
  • 2.when any technology that is not relied upon is turned off in a user agent, and
  • 3.when any technology that is not relied upon is not supported by a user agent

In addition, the following success criteria apply to all content on the page, including content that is not otherwise relied upon to meet conformance, because failure to meet them could interfere with any use of the page:

  • 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.

Note: If a page cannot conform (for example, a conformance test page or an example page), it cannot be included in the scope of conformance or in a conformance claim.

For more information, including examples, see Understanding Conformance Requirements.

Conformance Claims (Optional)

Conformance is defined only for Web pages. However, a conformance claim may be made to cover one page, a series of pages, or multiple related Web pages.

Required Components of a Conformance Claim

Conformance claims are not required. Authors can conform to WCAG 2.0 without making a claim. However, if a conformance claim is made, then the conformance claim must include the following information:

  • 1. Date of the claim
  • 2. Guidelines title, version and URI "Web Content Accessibility Guidelines 2.0 at http://www.w3.org/TR/2008/REC-WCAG20-20081211/"
  • 3. Conformance level satisfied: (Level A, AA or AAA)
  • 4. A concise description of the Web pages, such as a list of URIs for which the claim is made, including whether subdomains are included in the claim.Note 1: The Web pages may be described by list or by an expression that describes all of the URIs included in the claim. Note 2: Web-based products that do not have a URI prior to installation on the customer's Web site may have a statement that the product would conform when installed.
  • 5.A list of the Web content technologies relied upon.

Note: If a conformance logo is used, it would constitute a claim and must be accompanied by the required components of a conformance claim listed above.

Optional Components of a Conformance Claim

In addition to the required components of a conformance claim above, consider providing additional information to assist users. Recommended additional information includes:

  • A list of success criteria beyond the level of conformance claimed that have been met. This information should be provided in a form that users can use, preferably machine-readable metadata.
  • A list of the specific technologies that are "used but not relied upon."
  • A list of user agents, including assistive technologies that were used to test the content.
  • Information about any additional steps taken that go beyond the success criteria to enhance accessibility.
  • A machine-readable metadata version of the list of specific technologies that are relied upon.
  • A machine-readable metadata version of the conformance claim.

Note 1: Refer to Understanding Conformance Claims for more information and example conformance claims.

Note 2: Refer to Understanding Metadata for more information about the use of metadata in conformance claims.

Statement of Partial Conformance - Third Party Content

Sometimes, Web pages are created that will later have additional content added to them. For example, an email program, a blog, an article that allows users to add comments, or applications supporting user-contributed content. Another example would be a page, such as a portal or news site, composed of content aggregated from multiple contributors, or sites that automatically insert content from other sources over time, such as when advertisements are inserted dynamically.

In these cases, it is not possible to know at the time of original posting what the uncontrolled content of the pages will be. It is important to note that the uncontrolled content can affect the accessibility of the controlled content as well. Two options are available:

  • 1.A determination of conformance can be made based on best knowledge. If a page of this type is monitored and repaired (non-conforming content is removed or brought into conformance) within two business days, then a determination or claim of conformance can be made since, except for errors in externally contributed content which are corrected or removed when encountered, the page conforms. No conformance claim can be made if it is not possible to monitor or correct non-conforming content; OR
  • 2.A "statement of partial conformance" may be made that the page does not conform, but could conform if certain parts were removed. The form of that statement would be, "This page does not conform, but would conform to WCAG 2.0 at level X if the following parts from uncontrolled sources were removed." In addition, the following would also be true of uncontrolled content that is described in the statement of partial conformance:
    • a.It is not content that is under the author's control.
    • b.It is described in a way that users can identify (e.g., they cannot be described as "all parts that we do not control" unless they are clearly marked as such.)

Statement of Partial Conformance - Language

A "statement of partial conformance due to language" may be made when the page does not conform, but would conform if accessibility support existed for (all of) the language(s) used on the page. The form of that statement would be, "This page does not conform, but would conform to WCAG 2.0 at level X if accessibility support existed for the following language(s):"