When a container window is not shown, changes to the container's set of children do not necessarily trigger the immediate re-computation of the container's size and its chidlren's positions. Instead, the recalculation is delayed until the container is shown, which avoids redundant computations between a series of changes. The reflow-container method forces the immediate recalculation of the container's and its childrens's sizes and locations.
Immediately after calling the reflow-container method , get-width, get-height, get-x, and get-y report the correct size and location for the container and its children, even when the container is hidden.