How to add the wysiwyg on mission statement field?

See #608348: Getting a wysiwyg editor onto a system page. Core does not set input format selectors on all places where an input format is used, so Wysiwyg module does not know how to attach itself there.

Just so that others can easily find the information (this issue was to top search hit), I thought I'd share how I got this done.

By following the basic formula outlined in the issue linked from #1 and adding the relevant information from modules/system/system.admin.inc, I got the following function.

function mymodule_form_alter(&$form, &$form_state, $form_id) {
  if ($form_id == 'system_site_information_settings') {
    unset($form['site_mission']['#title']);
    unset($form['site_mission']['#type']);
    unset($form['site_mission']['#default_value']);
    unset($form['site_mission']['#description']);
    $form['site_mission']['site_mission'] = array(
      '#type' => 'textarea',
      '#title' => t('Mission'),
      '#default_value' => variable_get('site_mission', ''),
      '#description' => t("Your site's mission or focus statement (often prominently displayed on the front page)."),
    );
    $form['site_mission']['format'] = filter_form(2, NULL, array('message_format'));
  }
}

Just create a small custom module to house the function and enable it, and you'll have WYSIWYG on your site's mission field.

I've created a new module which implements this functionality: http://drupal.org/project/wysiwyg_extra