code: def Boolean(value, true=(u'yes', u'1', u'true'), false=(u'no', u'0', u'false'),
              encoding=None):
      
      value = Text(value, encoding)
      if value is not None:
          value = value.lower().strip()
      if value in true:
          return True
      elif value in false:
          return False
      return None
docs: Parse a value as a boolean.
  
      :type  value: `unicode` or `bytes`
      :param value: Text value to parse.
  
      :type  true: `tuple` of `unicode`
      :param true: Values to compare, ignoring case, for ``True`` values.
  
      :type  false: `tuple` of `unicode`
      :param false: Values to compare, ignoring case, for ``False`` values.
  
      :type  encoding: `bytes`
      :param encoding: Encoding to treat `bytes` values as, defaults to
          ``utf-8``.
  
      :rtype: `bool`
      :return: Parsed boolean or ``None`` if ``value`` did not match ``true`` or
          ``false`` values.