Understandable Principle
Definition
Information and user interface operation must be understandable.
Guidelines
1. Readability
- Declared page language
- Declared language parts
- Clear and simple text
html
<html lang="en">
<head>
...
</head>
<body>
<p>Text in English</p>
<p lang="fr">Texte en français</p>
</body>
</html>2. Predictability
- Consistent navigation
- Consistent identification
- No unexpected context changes
html
<!-- Good example -->
<button onclick="showDetails()" aria-expanded="false">Show more</button>
<!-- Bad example -->
<select onchange="submit()">
<!-- Unexpected context change -->
</select>3. Input Assistance
- Error identification
- Instructions and labels
- Error prevention
html
<form>
<label for="email">Email:</label>
<input type="email" id="email" name="email" aria-describedby="email-help" required />
<span id="email-help">Expected format: example@domain.com</span>
</form>Best Practices
- Clear error messages
- Explicit instructions
- Visible user feedback
- Important action confirmations