A grbox (graphical box) wraps an arbitrary xpce
graphical so it can participate in the typesetting of a parbox.
The encapsulated graphical is displayed on the parbox device and
otherwise behaves like any other graphical. See class parbox
for an overview of the document rendering system.
tbox: it is placed
inline at the position where it appears in parbox<-content.
left The graphical is floated to the left margin of the
first free line and the remaining text flows around it.
right As left but anchored against the
right margin.
top, center, bottom Vertical
alignment relative to the baseline of the line on which the grbox sits
(see also the ABSTRACT_HBOX ascent/descent slots).
rubber for stretch/shrink behaviour.