Subform: Overflow cuts things off instead of resizing

Customer application window shows things being hidden when they overflow from the size of the subform. ⎕WC version renders the hidden things on resizing the window but eWC version just cuts things off.

Start by reproducing the overflow in a customer application window using an eWC subform, then compare its resizing behavior with the ⎕WC version described in the issue. Done means content that exceeds the subform size is no longer cut off and becomes visible when the window is resized.

Written by the indexing model from the issue text.