Gets the position and size of the visible region of a snip in snip coordinates.
If no snip is specified, then the position and size of the snip's editor are returned, instead, in editor coordinates.
See also get-view in editor-admin%.
If snip is not #f, the current visible region of the snip is installed in the boxes x, y, w, and h. The x and y values are relative to the snip's top-left corner. The w and h values may be larger than the snip itself.
If snip is #f, the total visible region of the snip's top-level display is returned in editor coordinates. Using #f for snip is anaologous to using #t for full? in get-view in editor-admin%.