What does post back mean?
Any fields that are enabled, disabled or pre-populated should do so without having the page post back. What does this post back means?
postback (note it is one word) is a term used by ASP and JSF to describe a form which post to the same URL. It is Microsoft's way to pretend that variables on a web page can interact with each other like in event-driven desktop application, but I found it confusing because I know what really happens. SO has great explanation. For you it means that all widgets on the page should be enabled etc when page is first loaded, before clicking on submit button.