title: Validating an input in a Drupal form
body: <p>I have a Drupal form wherein someone inputs information, and I need to do a database query to check if it is valid before submitting.  I would like to either have a button the user can click to check the validity (or have it be done automatically after the user leaves that field), and then display some information about his selection.<br>
  I know I can use hook_form_submit to review a form when it is submitted and then stop the process if there are any errors, but I would like the user to be able to confirm they have selected the correct thing before submitting the form.</p>