Principle 3 - Understandable

Understandable: Information and the operation of user interface must be understandable.

Guideline 3.1 - Readable
Make text content readable and understandable.

• 3.1.1 - Language of Page [A]
  The default human language of each Web page can be programmatically determined. Understanding 3.1.1

• 3.1.2 - Language of Parts [AA]
  The human language of each passage or phrase in the content can be programmatically determined except for proper names, technical terms, words of indeterminate language, and words or phrases that have become part of the vernacular of the immediately surrounding text. Understanding 3.1.2

Guideline 3.2 - Predicable
Make Web pages appear and operate in predictable ways.

• 3.2.1 - On Focus [A]
  When any component receives focus, it does not initiate a change of context. Understanding 3.2.1

• 3.2.2 - On Input [A]
  Changing the setting of any user interface component does not automatically cause a change of context unless the user has been advised of the behavior before using the component. Understanding 3.2.2

• 3.2.3 - Consistent Navigation [AA]
  Navigational mechanisms that are repeated on multiple Web pages within a set of Web pages occur in the same relative order each time they are repeated, unless a change is initiated by the user.
  Understanding 3.2.3

• 3.2.4 - Consistent Identification [AA]
  Components that have the same functionality within a set of Web pages are identified consistently. Understanding 3.2.4

Guideline 3.3 - Input Assistance
Help users avoid and correct mistakes.

• 3.3.1 - Error Identification [A]
  If an input error is automatically detected, the item that is in error is identified and the error is described to the user in text. Understanding 3.3.1

• 3.3.2 - Labels or Instructions [A]
  Labels or instructions are provided when content requires user input. Understanding 3.3.2

• 3.3.3 - Error Suggestion [AA]
  If an input error is automatically detected and suggestions for correction are known, then the suggestions are provided to the user, unless it would jeopardize the security or purpose of the content.
  Understanding 3.3.3

• 3.3.4 - Error Prevention [AA]
  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:
  
  
  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. Understanding 3.3.4