code: function (token, errors, message, aggressive) {
      this.addErrorWithAcorn(token, function (ast, tokens) {
        var badPlus = [];
  
        acornWalk.simple(ast, {
          BinaryExpression: function (node) {
            if (!badPlus.length && node.operator === '+' && (aggressive || isString(node.left) || isString(node.right))) {
              badPlus.push(utils.getNextAcornToken(tokens, node.left.end));
            }
          }
        });
  
        return badPlus;
  
        function isString(node) {
          return node.type === 'Literal' && typeof node.value === 'string';
        }
      }, errors, message);
    }
docs: `aggressive` reports *any* addition as error.