Regex

		Sets or gets the regular expression used to validate the Node

		Arguments:
			regex {str} -- A standard regular expression string

		Raises:
			ValueError

		Returns:
			None | str

def regex(self, regex = None):
		"""Regex

		Sets or gets the regular expression used to validate the Node

		Arguments:
			regex {str} -- A standard regular expression string

		Raises:
			ValueError

		Returns:
			None | str
		"""

		# If regex was not set, this is a getter
		if regex is None:
			return self._regex

		# If the type is not a string
		if self._type != 'string':
			sys.stderr.write('can not set __regex__ for %s' % self._type)
			return

		# If it's not a valid string or regex
		if not isinstance(regex, (basestring, _REGEX_TYPE)):
			raise ValueError('__regex__')

		# Store the regex
		self._regex = regex