window.location.search returns the query string part of the current URL. All that bit of code is doing is ensuring the frame on the page gets passed the query

window.location.search returns the query string part of the current URL. All that bit of code is doing is ensuring the frame on the page gets passed the query string the outer page had. E.g. https://www.google.com/foobar/?hello https://www.google.com/foobar/?hello -> https://foobar.withgoogle.com/?hello https://foobar.withgoogle.com/?hello