docs: def visan(name=None):
      """
      Creates the grammar for a V-ISAN code.
  
      This is a variation on the ISAN (International Standard Audiovisual Number)
  
      :param name: name for the field
      :return: grammar for an ISRC field
      """
  
      if name is None:
          name = 'V-ISAN Field'
  
      field = pp.Regex('[0-9]{25}')
  
      field.setName(name)
  
      return field.setResultsName('visan')