append-to-registerappend-to-register is an interactive compiled Lisp function in `
register.el'. (append-to-register REGISTER START END &optional DELETE-FLAG) Append region to text in register REGISTER. With prefix arg, delete as well. Called from program, takes four args: REGISTER, START, END and DELETE-FLAG. START and END are buffer positions indicating what to append. Interactively, reads the register using `register-read-with-preview'.