code: def set_pkg_cr_text(self, doc, text):
          
          self.assert_package_exists()
          if not self.package_cr_text_set:
              self.package_cr_text_set = True
              doc.package.cr_text = text
          else:
              raise CardinalityError('Package::CopyrightText')
docs: Sets the package's license comment.
          Raises OrderError if no package previously defined.
          Raises CardinalityError if already set.