Introduction to two uses of iFrame tags in HTML_HTML/Xhtml_Web page production

There is a project I am currently working on - Butou Favorites. In short, it is to collect the pictures you like on the Butou page, which uses a lot of aspects about iframe. The summary is as follows:
　1. As a pop-up layer to cover

If you have done that kind of black mask that covers the entire page, and it happens that the user is using IE6, and it happens that there is a select element on the page, you will have a headache (the principle will not be repeated here) . We will find that the pop-up DIV cannot cover the selection, and it is our iframe's turn to appear. The logic is as follows:

Put it into an iframe at the same level as the pop-up div
Make sure the z-index of the iframe is smaller than the z-index of the pop-up div
Add window resize and scroll events to ensure that the iframe can cover the entire page

Part of the code

　2. Cross-domain writing cookie

There are two domains a.com and b.com. Under certain conditions, some functions of b will appear on page a. Sometimes it is necessary to perform some operations on the cookie of b.com domain when operating page a to facilitate the user's next visit. We only need to add an iframe (dynamic or fixed) to page a, the src attribute points to a proxy page of page b, and perform cookie operations on this page.