code: def update_refstring(self, string):
          
          self.refstring = string
          self._lines = []
          self._contains_index = None
          self.changed = True
  
          #The only other references that become out of date are the contains
          #and preamble attributes which are determined by the parsers.
          #Assuming we did everything right with the rt update, we should be
          #able to just use the new contains index to update those.
          icontains = self.contains_index
          ichar = self.charindex(icontains, 0)
          self.preamble = string[:ichar]
          self.contains = string[ichar + 9:]
docs: Updates the refstring that represents the original string that
          the module was parsed from. Also updates any properties or attributes
          that are derived from the refstring.