Wood will expand and contract across the grain, and a wide panel made of solid wood could change width by a half of an inch, warping the door frame. By allowing the wood panel to float, it can expand and contract without damaging the door.
Put trimmed and cleaned green beans in the steamer basket, set over the boiling water, cover, and steam until tender to the bite, 3 to 5 minutes (depending, again, on how crisp or tender you like your green beans).
1 Full-grown means past the time these beans would be picked for eating at the table, canning, or preserving, but before the pods are dry.  Steam no more than 2 inches (5.1 cm) of green, snap, string, or wax beans in a wire rack or basket above a pot (or kettle) of boiling water for 15 to 20 minutes.