Code sample #8:

This creates a new button to reset the form and demonstrates how to give the button its own validation handler. Also, it places validation of the first and last name fields into the default validation function.

<?php

function my_module_menu() {
  $items = array();
  $items['my_module/form'] = array(
    'title' => t('My form'),
    'page callback' => 'my_module_form',
    'access arguments' => array('access content'),
    'description' => t('My form'),
    'type' => MENU_CALLBACK,
  );
  return $items;
}

function my_module_form() {
  return drupal_get_form('my_module_my_form');
}

function my_module_my_form($form_state) {
  $form['name'] = array(
    '#type' => 'fieldset',
    '#title' => t('Name'),
    '#collapsible' => TRUE,
    '#collapsed' => FALSE,
  );
  
  // Removes the #required property and 
  // uses the validation function instead.
  $form['name']['first'] = array(
    '#type' => 'textfield',
    '#title' => t('First name'),
    '#default_value' => "First name",
    '#description' => "Please enter your first name.",
    '#size' => 20,
    '#maxlength' => 20,
  );
  
  // Removes the #required property and 
  // uses the validation function instead.
  $form['name']['last'] = array(
    '#type' => 'textfield',
    '#title' => t('Last name'),
  );
  $form['year_of_birth'] = array(
    '#type' => 'textfield',
    '#title' => "Year of birth",
    '#description' => 'Format is "YYYY"',
  );  
  $form['submit'] = array(
    '#type' => 'submit',
    '#value' => 'Submit',
  );
  // Adds a new button to clear the form. The #validate property
  // directs the form to use a new validation handler function in place
  // of the default.
  $form['clear'] = array(
    '#type' => 'submit',
    '#value' => 'Reset form',
    '#validate' => array('my_module_my_form_clear'),
  );
  
  return $form;
}

// This is the new validation handler for our Reset button. Setting
// the $form_state['rebuild'] value to TRUE, clears the form and also
// skips the submit handler.
function my_module_my_form_clear($form, &$form_state) {
	$form_state['rebuild'] = TRUE;
}

// Provides the first and last name fields to be required by using the 
// validation function to make sure values have been entered. This 
// causes the name fields to show up in red if left blank after clearing 
// the form with the "Reset form" button.
function my_module_my_form_validate($form, &$form_state) {
	$year_of_birth = $form_state['values']['year_of_birth'];
	$first_name = $form_state['values']['first'];
	$last_name = $form_state['values']['last'];
	if (!$first_name) {
		form_set_error('first', 'Please enter your first name.');
	}
	if (!$last_name) {
		form_set_error('last', 'Please enter your last name.');
	}
	if ($year_of_birth && ($year_of_birth < 1900 || $year_of_birth > 2000)) {
		form_set_error('year_of_birth', 'Enter a year between 1900 and 2000.');
	}
}

function my_module_my_form_submit($form, &$form_state) {
	drupal_set_message(t('The form has been submitted.'));
}
?>