Search API doc has some problems

In Drupal 7, a particular module's implementation of hook_update_index() only actually runs if search.module is enabled, and also if on the Search configuration page, your module has been enabled as an active Search module.

See http://api.drupal.org/api/function/search_cron/7 :

  foreach(variable_get('search_active_modules', array('node', 'user')) as $module) {
    // Update word index
    module_invoke($module, 'update_index');
  }

This needs to be documented on http://api.drupal.org/api/function/hook_update_index/7 -- Currently it just says hook_update_index runs in every cron run. This should probably also be documented on the module update guide, as it is a change from Drupal 6 behavior (and I have one data point, myself, of a module developer being caught by it).