The generic function
takes a description of a layout's child, and returns the geometry object associated with that child. It is called by interpret-description to parse individual children in a layout.
The default method accepts a child-desc argument which can be a pane (subclass of simple-pane or pinboard-object), a geometry object, or a symbol naming a slot in the interface which contains such a pane.
CAPI Reference Manual - 15 Dec 2011