Last updated October 22, 2018

When defining a new FormElement plugin, or if your constraints are only relevant for a single element, you can use the #element_validate property of an individual element to specify additional validation callbacks.

In this tutorial we'll:

  • Add an #element_validate callback to a single element in a form to perform validation of just that element.

By the end of this tutorial you should know how to add #element_validate callbacks to any form element in Drupal.