Principle 3 - Understandable

Guideline 3.1 - Readable

Make text content readable and understandable.

3.3.1 - Language of Page - Level A
All English language pages should have <html lang=“en”> set.

3.1.2 - Language of Parts - Level AA
If another language is used on the page, set lang=“language_code” in that container.

Guideline 3.2 - Predicable

Make Web pages appear and operate in predictable ways.

3.2.1 - On Focus - Level A
Do not intentionally break focus.
Do not cause applications to change on focus.

3.2.2 - On Input - Level A
Do not submit forms automatically.
Do not open a new window via a checkbox, radio button, select option, etc.

3.2.3 - Consistent Navigation - Level AA
Navigation items should be consistently located, and the order should not change while interacting with the website.

3.2.4 - Consistent Identification - Level AA
Use consistent actions/naming. For example, 2 links on a webpage that go to the same URL should have the same link text. 

Guideline 3.3 - Input Assistance

Help users avoid and correct mistakes.

3.3.1 - Error Identification - Level A
HTML 5 form validation is preferable.
Use shiv to load functionality for older browsers.

3.3.2 - Labels or Instructions - Level A
Always use labels and placeholder texts.

3.3.3 - Error Suggestion - Level AA
Error messages should clearly identify what is wrong.

3.3.4 - Error Prevention (Legal, Financial, Data) - Level AA
If any forms contain legal, financial, or data deletion, the user must be given a review/confirmation screen before submitting.