# 3 Understandable

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

## Guidelines

### 3.1 Readable

Make text content readable and understandable.

- [3.1.1 Language of Page](3.1.1-language-of-page.html) — The default human language of each web page can be programmatically determined. (Level A)
- [3.1.2 Language of Parts](3.1.2-language-of-parts.html) — 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. (Level AA)
- [3.1.3 Unusual Words](3.1.3-unusual-words.html) — A mechanism is available for identifying specific definitions of words or phrases used in an unusual or restricted way, including idioms and jargon. (Level AAA)
- [3.1.4 Abbreviations](3.1.4-abbreviations.html) — A mechanism for identifying the expanded form or meaning of abbreviations is available. (Level AAA)
- [3.1.5 Reading Level](3.1.5-reading-level.html) — When text requires reading ability more advanced than the lower secondary education level after removal of proper names and titles, supplemental content, or a version that does not require reading ability more advanced than the lower secondary education level, is available. (Level AAA)
- [3.1.6 Pronunciation](3.1.6-pronunciation.html) — A mechanism is available for identifying specific pronunciation of words where meaning of the words, in context, is ambiguous without knowing the pronunciation. (Level AAA)

### 3.2 Predictable

Make web pages appear and operate in predictable ways.

- [3.2.1 On Focus](3.2.1-on-focus.html) — When any user interface component receives focus, it does not initiate a change of context. (Level A)
- [3.2.2 On Input](3.2.2-on-input.html) — 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. (Level A)
- [3.2.3 Consistent Navigation](3.2.3-consistent-navigation.html) — 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. (Level AA)
- [3.2.4 Consistent Identification](3.2.4-consistent-identification.html) — Components that have the same functionality within a set of web pages are identified consistently. (Level AA)
- [3.2.5 Change on Request](3.2.5-change-on-request.html) — Changes of context are initiated only by user request or a mechanism is available to turn off such changes. (Level AAA)
- [3.2.6 Consistent Help](3.2.6-consistent-help.html) — If a web page contains any of the following help mechanisms, and those mechanisms are repeated on multiple web pages within a set of web pages, they occur in the same order relative to other page content, unless a change is initiated by the user: (Level A)

### 3.3 Input Assistance

Help users avoid and correct mistakes.

- [3.3.1 Error Identification](3.3.1-error-identification.html) — 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. (Level A)
- [3.3.2 Labels or Instructions](3.3.2-labels-or-instructions.html) — Labels or instructions are provided when content requires user input. (Level A)
- [3.3.3 Error Suggestion](3.3.3-error-suggestion.html) — 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. (Level AA)
- [3.3.4 Error Prevention (Legal, Financial, Data)](3.3.4-error-prevention-legal-financial-data.html) — 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)
- [3.3.5 Help](3.3.5-help.html) — Context-sensitive help is available. (Level AAA)
- [3.3.6 Error Prevention (All)](3.3.6-error-prevention-all.html) — For web pages that require the user to submit information, at least one of the following is true: (Level AAA)
- [3.3.7 Redundant Entry](3.3.7-redundant-entry.html) — Information previously entered by or provided to the user that is required to be entered again in the same process is either: (Level A)
- [3.3.8 Accessible Authentication (Minimum)](3.3.8-accessible-authentication-minimum.html) — A cognitive function test (such as remembering a password or solving a puzzle) is not required for any step in an authentication process unless that step provides at least one of the following: (Level AA)
- [3.3.9 Accessible Authentication (Enhanced)](3.3.9-accessible-authentication-enhanced.html) — A cognitive function test (such as remembering a password or solving a puzzle) is not required for any step in an authentication process unless that step provides at least one of the following: (Level AAA)