This is adding another configuration option to prevent the mixed mode popup when running under ie6/7 it is essentially just providing a way to specify a hosted (ideally blank) page on https so the default source for the frame in those browsers does not cause a security popup. There are dozens of threads about this if you google it but here is one http://www.ladysign-apps.com/blog/code/html/https-internet-explorer-nonsecure-popup/