If you set a form, page or container to read only all of the controls contained within them will also be read only.
>Is there a general rule that summarizes what the relations are, and a general rule how to approach the setting of individual controls in the relationship?>
It really boils down to what makes sense for your application. It takes a bit of forethought...and probably some trial and error to figure out what the best combination is for a particular form.
Regards,
Kevin McNeish Eight-Time .NET MVP VFP and iOS Author, Speaker & Trainer Oak Leaf Enterprises, Inc. Chief Architect, MM Framework http://www.oakleafsd.com