change-children in area-container<%>

Takes a filter procedure and changes the container's list of active children. The filter procedure takes a list of children areas and returns a new list of children areas. The new list must consist of children that were created as subareas of this area (i.e., change-children cannot be used to change the parent of a subarea).

After the set of active children is changed, the container computes the sets of newly inactive and newly active children. Newly inactive windows are hidden. Newly active windows are shown.

Since non-window areas cannot be hidden, non-window areas cannot be made inactive. If the filter procedure removes non-window subareas, an exception is raised and the set of active children is not changed.

• (send an-area-container change-children filter) -> void
     filter : procedure of one argument, a list of subarea<%> objects, that returns a list of subarea<%> objects