This function returns a list of all existing devices.
— Function: device-or-frame-p object
This function returns non-nil if object is a device or
frame. This function is useful because devices and frames are similar
in many respects and many functions can operate on either one.
— Function: device-frame-list &optional device
This function returns a list of all frames on device.
device defaults to the currently selected device.
— Function: frame-device &optional frame
This function returns the device that frame is on.
frame defaults to the currently selected frame.