principle: Understandable
Make sure that everyone can understand or comprehend the same content and components. Can people understand this content with whatever capacity they have?
3.1.1 Language of Page
Each page must have a <html lang=""> attribute that matches the main language of the page.
3.1.2 Language of Parts
Any parts of the content in a different language must be marked with the correct lang attribute. Expressions borrowed from another language (like “déjà vu” in English) do not need this, unless pronunciation or understanding would be affected.
3.1.3 Unusual Words
Unusual terms, jargon, or figurative language should be avoided when possible, or explained the first time they appear.
3.1.4 Abbreviations
Abbreviations and acronyms should be avoided when possible, or explained the first time they appear.
3.1.5 Reading Level
If content requires reading skills above lower secondary education (around 9th grade), provide a simpler version, a summary, a visual aid, or a spoken version to help with understanding.
3.1.6 Pronunciation
If a word can be pronounced in different ways with different meanings, the intended meaning must be clarified to avoid confusion or ambiguity.
3.2.1 On Focus
No unexpected changes must happen when an element receives focus (like open a popup, move focus, submit a form).
3.2.2 On Input
No unexpected changes must happen when a field value changes (like auto-submit, reload, open new page).
3.2.3 Consistent Navigation
Navigation elements (like menus, links, search) must appear in the same place and order across pages.
3.2.4 Consistent Identification
Elements with the same function must look, behave, and be labeled the same way across pages.
