1. First task was to create a list for the customer which had "Order Date" and "Processed Date"
so here is it:
3. Now that the snippet is ready I need to find a way to include this to the "NewForm.aspx" and also to "EditForm.aspx", Initially I though of using SharePoint Designer to do this, but somehow though there could be an easier way. Finally after 3 days and sevral cups of tea I found that I can add a content editor webpart the "NewForm.aspx" and "Editform.aspx" page . Normally "Edit Page" option is grayed out for these pages. But there is a cheat to get in
Just append "ToolPaneView=2" to the end of the URL for example
5. Now it is time for testing, first I tried to key in a "Processed date" before the "Order Date" and as you can see I got a pop up "The Processed Date should be between Order Date and Todays Date" Bingo!!
6. The second thing I need to test what happens if I choose a date later that todays date.