I have a simple example but I look for a general principle in how to do.
I have a web form, webform1, with a lable control Lable1. From webform1 I open a popup, popup1, with e.g.
window.open('Test.aspx', '_blank', 'width=900,height=450,top=312,left=190,scrollbars=1')
in the script section:
With the popup1 open and active, my question is how can I in popup1 make a change to Lable1 in webform1?