What is HTML <select> required Attribute

This is An HTML form with a required drop-down list.

index.html

Example: HTML

<form action="/action_page.php">
  <label for="cars">Choose a car:</label>
  <select name="cars" id="cars" required>
    <option value="">None</option>
    <option value="volvo">Volvo</option>
    <option value="saab">Saab</option>
    <option value="mercedes">Mercedes</option>
    <option value="audi">Audi</option>
  </select>
  <br><br>
  <input type="submit" value="Submit">
</form>

Output should be:

Type:	html
Category:	Web Tutorial
Sub Category:	HTML Tag
Uploaded by:	Admin