code: def _set_extensions(self):
          
  
          self._critical_extensions = set()
  
          for extension in self['single_extensions']:
              name = extension['extn_id'].native
              attribute_name = '_%s_value' % name
              if hasattr(self, attribute_name):
                  setattr(self, attribute_name, extension['extn_value'].parsed)
              if extension['critical'].native:
                  self._critical_extensions.add(name)
  
          self._processed_extensions = True
docs: Sets common named extensions to private attributes and creates a list
          of critical extensions