Alist of elements (NAME . CONTENTS), one for each Emacs register.
NAME is a character (a number). CONTENTS is a string, number, marker, list
or a struct returned by `registerv-make'.
A list of strings represents a rectangle.
A list of the form (file . FILE-NAME) represents the file named FILE-NAME.
A list of the form (file-query FILE-NAME POSITION) represents
position POSITION in the file named FILE-NAME, but query before
visiting it.
A list of the form (WINDOW-CONFIGURATION POSITION)
represents a saved window configuration plus a saved value of point.
A list of the form (FRAME-CONFIGURATION POSITION)
represents a saved frame configuration plus a saved value of point.