As the search form collates keys from other modules hooked in via hook_form_alter, the validation takes place in _submit. search_form_validate() is used solely to set the 'processed_keys' form value for the basic search form.

File

drupal-7.x/modules/search/search.pages.inc, line 143

User page callbacks for the search module.

Code

function search_form_validate($form, &$form_state) {
  form_set_value($form['basic']['processed_keys'], trim($form_state['values']['keys']), $form_state);
}