materio-base-d7/sites/all/modules/contrib/seo/metatag/metatag_hreflang/metatag_hreflang.install

<?php
/**
 * @file
 * Various update scripts for Metatag:hrelang.
 */

/**
 * Implements hook_requirements().
 */
function metatag_hreflang_requirements($phase) {
  $requirements = array();
  // Ensure translations don't break during installation.
  $t = get_t();

  if ($phase == 'runtime') {
    // Check if the Alternative Hreflang module is present.
    if (module_exists('hreflang')) {
      $requirements['metatag_hreflang'] = array(
        'severity' => REQUIREMENT_ERROR,
        'title' => 'Metatag',
        'value' => $t('The Metatag:hreflang module should not be used at the same time as the hreflang module.'),
        'description' => $t('If both the Metatag:hreflang module and the Alternative Hreflang (hreflang) module are used at the same time it is likely that they will output duplicate meta tags. As a result, it is recommended to only use one at a time.'),
      );
    }
  }

  return $requirements;
}

/**
 * Implements hook_uninstall().
 */
function metatag_hreflang_uninstall() {
  // Delete any custom variables that are used.
  variable_del('metatag_hreflang_allow_dupe');
}