As a man who enjoys coding solutions, I'll run into a frustrating problem every once in a great while: sharing information between two different domains. Suppose you have an e-commerce funnel on one domain, ABC.com, while your main site lives on XYZ.com. Your boss decides that he or she wants to see user interaction after a product is added to the cart, but before a purchase is made. Perhaps users can be directed towards certain information on XYZ.com after a card add to assist a purchase. However...
Of course not!
You might be wondering, "If I create an IFrame on ABC.com, won't my page on XYZ.com look a little... out of sorts?" Fortunately, IFrames have an attribute that allows them to be hidden. The end result? The browser makes requests to "load" the other page without rendering any of the content. Unless the user is especially savvy, he or she will be none the wiser that the transaction is even taking place. If a custom page is used on XYZ.com that only contains the tracking code, the bandwidth used will be extremely small. The XYZ.com domain will know that a cart add was made, and the interactions will be tracked for future analysis.
To recap, IFrames provide a vehicle to support a client/server sort of transaction that allows one domain to communicate information to another. I have personally tested on both FireFox and IE and have enjoyed the results.
That's all I have for now. Happy coding, friends!