hook_form_FORM_ID_alter(&$form, &$form_state)Provide a form-specific alteration instead of the global hook_form_alter().
Modules can implement hook_form_FORM_ID_alter() to modify a specific form, rather than implementing hook_form_alter() and checking the form ID, or using long switch statements to alter multiple forms.
Note that this hook fires before hook_form_alter(). Therefore all implementations of hook_form_FORM_ID_alter() will run before all implementations of hook_form_alter(), regardless of the module order.
$form Nested array of form elements that comprise the form.
$form_state A keyed array containing the current state of the form.
modules/system/system.api.php, line 782
<?php
function hook_form_FORM_ID_alter(&$form, &$form_state) {
// Modification for the form with the given form ID goes here. For example, if
// FORM_ID is "user_register_form" this code would run only on the user
// registration form.
// Add a checkbox to registration form about agreeing to terms of use.
$form['terms_of_use'] = array(
'#type' => 'checkbox',
'#title' => t("I agree with the website's terms and conditions."),
'#required' => TRUE,
);
}
?>