Dialog boxes can be divided into modal dialog boxes and modeless dialog boxes. The difference between the two is whether the user can work elsewhere in the same application before the dialog box is closed. For example: the open file dialog box is a typical modal dialog box. After you select the file to open and press OK, or after canceling the file opening operation, you can perform other operations in the same application. The common find and replace dialog box is a typical modeless dialog box. While the dialog box is open, we can also perform other work. Modal dialog boxes always maintain focus. You cannot switch windows unless you close the dialog box. A modeless dialog box does not always maintain focus, but it always remains on top.
Full guide to pop-up web window (html/hta)
1. Pop up a full-screen window