Techniques for WCAG 2.0

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# G174: Providing a control with a sufficient contrast ratio that allows users to switch to a presentation that uses sufficient contrast

## Applicability

Any technology.

This technique relates to:

- Success Criterion 1.4.3 (Contrast (Minimum))
  - How to Meet 1.4.3 (Contrast (Minimum))
  - Understanding Success Criterion 1.4.3 (Contrast (Minimum))
- Success Criterion 1.4.6 (Contrast (Enhanced))
  - How to Meet 1.4.6 (Contrast (Enhanced))
  - Understanding Success Criterion 1.4.6 (Contrast (Enhanced))
- Conformance Requirement 1 (Conformance Level)

## Description

When the contrast between the text and its background for some portion of the page has not been designed to meet the contrast level for Success Criterion 1.4.3 or 1.4.6, it is possible to meet these guidelines using the "Alternate Version" clause in the conformance requirements (Conformance Requirement 1). A link or control on the page can either change the page so that all aspects conform, or it could take the viewer to a new version of the page that does conform at the desired level.

For this technique to be used successfully, three things must be true.

1. The link or control on the original page must itself meet the contrast requirement of the desired SC. (If the user cannot see the control they may not be able to use it to go to the new page.)

2. The new page must contain all the same information and functionality as the original page.

3. The new page must conform to all of the SC for the desired level of conformance. (i.e., the new page cannot just have the desired level of contrast but otherwise not conform).

This technique can be used to meet Success Criterion 1.4.3 by having text (or images of text) on the alternate version of the page be 4.5:1 contrast and any large text (or images of large text) be 3:1 contrast with its background. If the alternate version of the page has all text (or images of text) with 7:1 contrast and large text (or images of large text) with 4.5:1 contrast then it would satisfy both Success Criterion 1.4.3 and 1.4.6.

Note: This technique can be used in combination with a style switching technique to present a page that is a conforming alternate version for non-conforming content. Refer to C29: Using a style switcher to provide a conforming alternate version (CSS) and Understanding Conforming Alternate Versions for more information.

## Examples

- A page with some headlines that do not meet the 3:1 contrast requirements has a high contrast (5:1) link at the top of the page that takes the user to a new version of the page with minimum 4.5:1 contrast on all text and images of text.

- A page uses shaded backgrounds for effect but results in text to background contrast of 4:1. A control at the top of the page says "high contrast". Clicking on it causes different styles to be used and dropping the background colors to achieve 7:1 contrast.

## Related Techniques

- G17: Ensuring that a contrast ratio of at least 7:1 exists between text (and images of text) and background behind the text
- G18: Ensuring that a contrast ratio of at least 4.5:1 exists between text (and images of text) and background behind the text
- G145: Ensuring that a contrast ratio of at least 3:1 exists between text (and images of text) and background behind the text
- G148: Not specifying background color, not specifying text color, and not using technology features that change those defaults

## Tests

### Procedure

1. Check that a link or control exists on the original page that provides access to the alternate version.

2. Check that the link or control on the original page conforms to all success criteria for the conformance level being tested.

3. Check that the alternate version meets the contrast and all other success criteria for the conformance level being tested.

### Expected Results

- All three checks are true.

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