A render-box corresponds to elements in a DOM tree.
Each box has a size, paddings, margins and borders. Boxes may have one or more childs.
While all nodes may have a position or dimensions, boxes are special, as they can have borders, margins and paddings. Borders, paddings and margins can have percentages, the margins can additionally be 'auto'.
The StrictInset variables for these properties contain the resolved values, while the box-definition contain the unresolved values. The resolve values are not valid unless the object has been validated to least least 'LAYOUTING'.
@author Thomas Morgner