frameset-frame-id

frameset-frame-id is an autoloaded compiled Lisp function in `frameset.el'.

(frameset-frame-id FRAME)

Return the frame id of FRAME, if it has one; else, return nil.
A frame id is a string that uniquely identifies a frame.
It is persistent across `frameset-save' / `frameset-restore'
invocations, and once assigned is never changed unless the same
frame is duplicated (via `frameset-restore'), in which case the
newest frame keeps the id and the old frame's is set to nil.