code: function(node) {
  				var lhs = node.left,
  					affectsProto;
  
  				if (lhs.type !== "MemberExpression" || lhs.object.type !== "MemberExpression") {
  					return;
  				}
  
  				affectsProto = lhs.object.computed ?
  					lhs.object.property.type === "Literal" && lhs.object.property.value === "prototype" :
  					lhs.object.property.name === "prototype";
  
  				if (!affectsProto) {
  					return;
  				}
  
  				modifiedBuiltins.forEach(function(builtin) {
  					if (lhs.object.object.name === builtin) {
  						context.report(node, ProblemMessages.noExtendNative, {builtin: builtin});
  					}
  				});
  			}
docs: handle the Array.prototype.extra style case