code: def set_pkg_summary(self, doc, text):
          
          self.assert_package_exists()
          if not self.package_summary_set:
              self.package_summary_set = True
              doc.package.summary = text
          else:
              raise CardinalityError('Package::Summary')
docs: Set's the package summary.
          Raises CardinalityError if summary already set.
          Raises OrderError if no package previously defined.