(hdefine geometry|camera|window|appearance|image|transform|ntransform name value)Sets the value of a handle of a given type.
(hdefine <type> <name> <value>)
is generally equivalent to
(read <type> { define <name> <value> })
except that the assignment is done when hdefine is executed, (possibly
not at all if inside a conditional statement), while the read
… define performs assignment as soon as the text is
read. See Embedded objects and external-object references. See (read …). See (hdelete …).