public interface EdgeSizes
defaultSize will map to
 the default edge size or  offset for the canvas (Canvas.edgeSize,
 or Canvas.edgeOffset and top, left,
 right and bottom will map to the edgeTop/edgeOffsetTop,  edgeLeft/edgeOffsetLeft, edgeRight/edgeOffsetRight, and edgeBottom/edgeOffsetBottom attributes on the paneContainer
 respectively. Note that not all these properties have to be set - if unset standard edge sizing rules will apply.