Geometry RESTRICT and JOIN

I'm trying to add all the "box op point" operators. The C routines are
written and working as advertised. The manuals description of the
RESTRICT and JOIN clauses of CREATE OPERATOR don't seem too clear. Are
these samples correct, or am I totally off base here?

CREATE OPERATOR << (
LEFTARG = box,
RIGHTARG = point,
PROCEDURE = leftof,
RESTRICT = scalarltsel, -- ?? UNSURE
JOIN = positionjoinsel -- ?? UNCLEAR
);

CREATE OPERATOR &> (
LEFTARG = box,
RIGHTARG = point,
PROCEDURE = notleft,
RESTRICT = scalargtsel, -- ?? UNSURE
JOIN = positionjoinsel -- ?? UNCLEAR
);

CREATE OPERATOR @> (
LEFTARG = box,
RIGHTARG = point,
PROCEDURE = contains,
RESTRICT = eqsel, -- ?? UNSURE
JOIN = contjoinsel -- ?? UNCLEAR
);

...etc...