Value is the value of window property PROP on FRAME.
If FRAME is nil or omitted, use the selected frame.
On X Windows, the following optional arguments are also accepted:
If TYPE is nil or omitted, get the property as a string.
Otherwise TYPE is the name of the atom that denotes the type expected.
If SOURCE is non-nil, get the property on that window instead of from
FRAME. The number 0 denotes the root window.
If DELETE-P is non-nil, delete the property after retrieving it.
If VECTOR-RET-P is non-nil, don't return a string but a vector of values.
On MS Windows, this function accepts but ignores those optional arguments.
Value is nil if FRAME hasn't a property with name PROP or if PROP has
no value of TYPE (always string in the MS Windows case).
(fn PROP &optional FRAME TYPE SOURCE DELETE-P VECTOR-RET-P)