code: def help_text(self):
      
      result = []
      for name in sorted(self._declarations.keys()):
        result.append(name)
        result.append('-' * len(name))
        decl = self._declarations[name]
        if decl.description:
          result.append(decl.description.strip())
        else:
          result.append('(no description found)')
        if decl.has_default:
          result.append('')
          quotes = '"' if type(decl.default_value) is str else ''
          result.append('  default_value={quotes}{val}{quotes}'.format(
              quotes=quotes, val=decl.default_value))
        result.append('')
        result.append('')
      return '\n'.join(result)
docs: Return a string with all config keys and their descriptions.