ePiX markers are called
by name: 
spot(P pt); dot(P pt); ddot(P pt);
box(P pt); bbox(P pt);
ring(P pt); circ(P pt);
spot and (d)dot are solid dots that cannot be colored.
box and bbox are solid, colorable squares. A
ring is colorable and transparent, while a circ is
uncolorable and opaque. Markers in the same column are the same size,
and each column is 1.5 times the diameter of the next. The diameter of
a dot (hence that of all the above markers) is set with
dot_size(diam). The argument, 3 by default, is a number
of pt. The glyphs listed in Table 2.1 are
available via the command
marker(P pt, <MARKER TYPE>);
