App Interface Guideline: Forms — Inline Validation. Keywords: onBlur validation. Platform: iOS/Android/React Native. Description: Validate inputs on blur or submit with clear messaging. Do: Validate onBlur and onSubmit. Don't: Validate on every keystroke causing jank. Good Example: onBlur={() => validateEmail(value)}. Bad Example: onChangeText={v => validateEmail(v)} // every char. Severity: Medium.