code: function checkForDisallowedCharactersInString(node, identifier) {
          if (typeof identifier !== "undefined" && isNotAllowed(identifier)) {
              context.report(node, "Unexpected umlaut in \"" + identifier + "\".");
          }
      }
docs: Check if function has a underscore at the end
  @param {ASTNode} node node to evaluate
  @returns {void}
  @private