A static properties collection. That one is static; once computed it does not change anymore. It does not (under no thinkable circumstances) depend on the given content. It may depend on static content of the parent.
A box typically has two sets of margins. The first set is the declared margin set - it simply expresses the user's definitions. The second set is the effective margin set, it is based on the context of the element in the document tree and denotes the distance between the nodes edge and any oposite edge.
@author Thomas Morgner