frame-creation-function-alist

frame-creation-function-alist is a variable defined in `frame.el'.
Its value is

((x . x-create-frame-with-faces)
 (nil . tty-create-frame-with-faces))

Documentation:
Method for window-system dependent functions to create a new frame.
The window system startup file should add its frame creation
function to this method, which should take an alist of parameters
as its argument.