The invalidate-pane-constraints function is used to cause the resizing of a pane if its minimum and maximum size constraints have changed. It returns t if resizing was necessary.
This function informs the CAPI that pane 's constraints (its minimum and maximum size) may have changed. The CAPI then checks this, and if the pane is no longer within its constraints it resizes it so that it is and then makes the pane's parent layout lay its children out and display them again at their new positions and sizes. If the pane is resized, then invalidate-pane-constraints returns t .