x-change-window-property

x-change-window-property is a built-in function in `C source code'.

(x-change-window-property PROP VALUE &optional FRAME TYPE FORMAT OUTER-P)

Change window property PROP to VALUE on the X window of FRAME.
PROP must be a string. VALUE may be a string or a list of conses,
numbers and/or strings. If an element in the list is a string, it is
converted to an atom and the value of the atom is used. If an element
is a cons, it is converted to a 32 bit number where the car is the 16
top bits and the cdr is the lower 16 bits.

FRAME nil or omitted means use the selected frame.
If TYPE is given and non-nil, it is the name of the type of VALUE.
If TYPE is not given or nil, the type is STRING.
FORMAT gives the size in bits of each element if VALUE is a list.
It must be one of 8, 16 or 32.
If VALUE is a string or FORMAT is nil or not given, FORMAT defaults to 8.
If OUTER-P is non-nil, the property is changed for the outer X window of
FRAME. Default is to change on the edit X window.