Understanding WCAG 2.0

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Error Prevention (Legal, Financial, Data):
Understanding SC 3.3.4

3.3.4 Error Prevention (Legal, Financial, Data): For Web pages that cause legal commitments or financial transactions for the user to occur, that modify or delete user-controllable data in data storage systems, or that submit user test responses, at least one of the following is true: (Level AA)

  1. Reversible: Submissions are reversible.

  2. Checked: Data entered by the user is checked for input errors and the user is provided an opportunity to correct them .

  3. Confirmed: A mechanism is available for reviewing, confirming, and correcting information before finalizing the submission .

Intent of this Success Criterion

The intent of this Success Criterion is to help users with disabilities avoid serious consequences as the result of a mistake when performing an action that cannot be reversed. For example, purchasing non-refundable airline tickets or submitting an order to purchase stock in a brokerage account are financial transactions with serious consequences. If a user has made a mistake on the date of air travel, he or she could end up with a ticket for the wrong day that cannot be exchanged. If the user made a mistake on the number of stock shares to be purchased, he or she could end up purchasing more stock than intended. Both of these types of mistakes involve transactions that take place immediately and cannot be altered afterwards, and can be very costly. Likewise, it may be an unrecoverable error if users unintentionally modify or delete data stored in a database that they later need to access, such as their travel profile in a travel services Web site. Test data is included in this provision because, in order for tests to be valid, users are not allowed to modify their answers once submitted; so users need to be able to ensure that their submission is correct.

Users with disabilities may be more likely to make mistakes. People with reading disabilities may transpose numbers and letters, and those with motor disabilities may hit keys by mistake. Providing the ability to reverse actions allows users to correct a mistake that could result in serious consequences. Providing the ability to review and correct information gives the user an opportunity to detect a mistake before taking an action that has serious consequences.

User-controllable data is data that is intended to be accessed by users. (e.g., name and address for the user's account.) It does not refer such things as internet logs and search engine monitoring data.

Specific Benefits of Success Criterion 3.3.4:

  • Providing safeguards to avoid serious consequences resulting from mistakes helps users with all disabilities who may be more likely to make mistakes.

Examples of Success Criterion 3.3.4

Related Resources

Resources are for information purposes only, no endorsement implied.

(none currently documented)

Techniques and Failures for Success Criterion 3.3.4 - Error Prevention (Legal, Financial, Data)

Each numbered item in this section represents a technique or combination of techniques that the WCAG Working Group deems sufficient for meeting this Success Criterion. The techniques listed only satisfy the Success Criterion if all of the WCAG 2.0 conformance requirements have been met.

Sufficient Techniques

Instructions: Select the situation below that matches your content. Each situation includes techniques or combinations of techniques that are known and documented to be sufficient for that situation.

Situation A: If an application causes a legal transaction to occur, such as making a purchase or submitting an income tax return:

  1. Providing a stated period of time after submission of the form when the order can be updated or canceled by the user (future link)

  2. G98: Providing the ability for the user to review and correct answers before submitting

  3. Having a checkbox in addition to a submit button (future link)

Situation B: If an action causes information to be deleted:

  1. G99: Providing the ability to recover deleted information

  2. Providing a dialog to the user which requires confirmation before information is deleted (future link)

  3. Requiring a user to select a confirmation checkbox before submitting an action that causes information to be deleted (future link)

  4. Having a checkbox in addition to a submit button (future link)

Situation C: If the Web page includes a testing application:

  1. G98: Providing the ability for the user to review and correct answers before submitting

  2. Asking for confirmation before final submission (future link)

Additional Techniques (Advisory) for 3.3.4

Although not required for conformance, the following additional techniques should be considered in order to make content more accessible. Not all techniques can be used or would be effective in all situations.

Failures for SC 3.3.4

The following are common mistakes that are considered failures of Success Criterion 3.3.4 by the WCAG Working Group.

(No failures currently documented)

Key Terms

input error

information provided by the user that is not accepted

Note: This includes:

  1. Information that is required by the Web page but omitted by the user

  2. Information that is provided by the user but that falls outside the required data format or values

legal commitments

transactions where the person incurs a legally binding obligation or benefit

Example: A marriage license, a stock trade (financial and legal), a will, a loan, adoption, signing up for the army, a contract of any type, etc.


process or technique for achieving a result

Note 1: The mechanism may be explicitly provided in the content, or may be relied on to be provided by either the platform or by user agents, including assistive technologies.

Note 2: The mechanism must meet all Success Criteria for the conformance level claimed.


series of user actions where each action is required in order to complete an activity

Example 1: Successful use of a series of Web pages on a shopping site requires users to view alternative products, prices and offers, select products, submit an order, provide shipping information and provide payment information.

Example 2: An account registration page requires successful completion of a Turing test before the registration form can be accessed.


data that is intended to be accessed by users

Note: This does not refer such things as internet logs and search engine monitoring data.

Example: Name and address fields for a user's account.