Robby was given a chair by his great grandmother when he was 2.
It was handed down to Miriam and now to Peggy, but he still feels
privileged to sit on it (though much too big).

Peggy asserts the chair is hers (after all, she is the only one of an
appropriate size for it). When Robby sat on it today, she became very
upset and, near tears, commended “Robby, offa chair!” The sense of
what she meant is very clear. How can one explain the surface features?