Principal manipulation method for the area occupied by a tile. Its
behaviour depends on the place of the tile in the hierarchy as well as
whether or not the tile is already tile<-enforced.
If the tile is not yet tile<-enforced,
the width and height components are used to set tile<-ideal_width
and tile<-ideal_heigth and the ideal sizes
are propagated over the tile hierarchy using tile->compute.
If the tile is already enforced, it will set the ideal size of this
tile. Next, it will change the stretch/shrink properties of all members
of the tile<-super
tile, such that all members before and upto (above, left of) this tile
have fixed size and all members after (below, right of) can be resized.
Used by
frame->event
to realise resizable subwindows.
