AChecker: Open Accessibility Checks
Goal
The goal of the Open Accessibility Checks (OAC) is to create a universal series of tests that may be applied to HTML pages to determine their compliance with accessibility standards. This is an open source project that can be used to support worldwide efforts to create accessible web material.
Current web accessibility checking tools all vary in the tests they use. This causes confusion to the user when each tool gives a different report on a page's accessibility status. It also weakens accessibility guidelines because there is no standard method of testing compliance. It is hoped that the OAC will provide a standard that every accessibility checking tool can implement and therefore provide a consistent accessibility rating to the user.
List Of Checks
All checks: sorted by trigger element
All checks: sorted by ID number
Status
These test are not specifically oriented towards any one accessibility standard but may be used by any standard that wishes to test for accessibility. Any accessibility standard can be made up using a subset of these checks.
Here is the current list of guidelines that are mapped to the checks. Note that these guidelines have not been sanctioned by their governing bodies.
Currently, these OAC standards have no status. In the future, the governing bodies that make up accessibility standards, such as the WAI or BITV, can give OAC standards an official status. In effect, stating that to comply with their standard an OAC set of accessibility tests must be passed.
These checks may be implemented by a human or any software accessibility checking tool. Current tools that have committed to supporting the OAC are:
- A-Prompt version 2
- ATRC Checker
- ht://Check
Check Description
Each check is descripted in a clear and unambiguous format. Anyone wishing to implement the check, using software or by human, should be able to easily do so.
Each check has a trigger element with an option to specify an attribute or content. For example, the check for image missing ALT text uses the IMG element as a trigger. If a check requires testing of the document's content it would use the BODY element as a trigger.
| Property | Value |
|---|---|
| Description | All IMG elements must have an ALT attribute. |
| ID Number | 1 |
| Status | proposed |
| Detection Confidence | high (known problem) |
| Trigger Element | IMG |
| Prerequisite Checks | None |
| Repair Text | Add an ALT attribute to your IMG element. Example: <IMG src="rex.jpg" alt="a picture of Rex the cat"/>. |
Each check has at least 2 associated test files. One test file contains an example of the accessibility problem that should fail the check. The other test file contains an example of HTML code that should pass the check.
Machine Use and Human Decisions
Each of these tests can be implemented by a software testing tool however user intervention may still be required. The tests have 3 levels of 'confidence' that the test result is accurate:
- high: The test has identified a known problem (e.g. image is missing an ALT attribute)
- medium: The test has identified a potential problem (e.g. ALT text is the same as the image file name)
- low: The test has identified a potential problem (e.g. image does not have an associated long description and may require one)
If a test with a high 'confidence' rating fails then no user intervention is required to determine that the test result is accurate. If a test fails with a 'medium' or 'low' confidence rating fails then user intervention is required to determine whether the result is accurate or not.
Creation Of Checks
Anyone may create an accessibility check and contribute it to the master list. Each governing body for an accessibility standard is free to accept or reject the check as part of their standard. To contribute a check, contact Chris Ridpath (chris.ridpath@utoronto.ca).
Automated Implementation
Each check is described in an XML file using a structured format. Here is the link to the schema for the XML file. This file may be machine read and the checks created dynamically. Here is a site that uses a Java servlet to read the current checks file and perform accessibility checking. This design allows for rapid implementation of new accessibility checks. (TODO - A more complete description of this system.)
The source code for this evaluator is available under an open source license. (TODO - provide a link for downloading the source).
The Open Accessibility Checks project is currently supported by the Adaptive TechnologyResource Center at the University Of Toronto.
July 15, 2004
