By default, the C1Accordion control's AllowCollapseAll property is set to True, meaning that all panes of an accordion can be collapsed by the user. This is useful in cases where you want to conserve screen real estate so that the user is free of unnecessary distractions. Think of it like the musical instrument accordion, which can be tightly compressed for storage and then decompressed when a player wants to use it.

But there are times when this won't fit into the design of your user interface. For example, you may want to use the accordion as a menu element. In that case, you'd want the C1Accordion control to fill to a specific height or width at all times, and the control won't fulfill that need if all of its panes can be collapsed. Therefore, you would set the AllowCollapseAll property to False so that one pane has to remain open at all times. You would then set the height or width property as desired and then set the C1Accordion.Fill property to True so that the C1Accordion control and its panes always fill to your specified height or width.