code: protected static function loadMimeAliases($aliasesFile)
      {
          if ($aliasesFile === null) {
              $aliasesFile = static::$mimeAliasesFile;
          }
          $aliasesFile = Yii::getAlias($aliasesFile);
          if (!isset(self::$_mimeAliases[$aliasesFile])) {
              self::$_mimeAliases[$aliasesFile] = require $aliasesFile;
          }
  
          return self::$_mimeAliases[$aliasesFile];
      }
docs: Loads MIME aliases from the specified file.
  @param string $aliasesFile the path (or alias) of the file that contains MIME type aliases.
  If this is not set, the file specified by [[mimeAliasesFile]] will be used.
  @return array the mapping from file extensions to MIME types
  @since 2.0.14