Q.Which HTML5 input attribute prevents a form from being submitted until the field has been filled in?
(A) pattern
(B) placeholder
(C) required
(D) readonly

This tests HTML5's built-in validation attributes and which one enforces that a field is not left empty. …

HTML5 can validate simple things using attributes on an input.

(A) pattern checks the entry against a rule (a regular expression) but does not, by itself, force the field to be filled — incorrect.

(B) placeholder only shows hint text inside an empty box; it is a guide, not validation — incorrect. …

Thinking placeholder validates input. Placeholder text is only a hint that disappears when the user t …