The Drupal form field required syntax

Drupal form fields FAQ: What is the syntax to make a Drupal form field (textfield, textarea, password field) required?

To make a Drupal form field required, just use the Drupal form #required attribute, as shown in this required textfield example:

$form['first_name'] = array(
  '#title' => t('First Name'),
  '#type' => 'textfield',
  '#required' => TRUE,

As you can see, to set a Drupal form field to be required, you just need to add the #required form attribute, and set it to TRUE.