undo-start

undo-start is a compiled Lisp function in `simple.el'.

(undo-start &optional BEG END)

Set `pending-undo-list' to the front of the undo list.
The next call to `undo-more' will undo the most recently made change.
If BEG and END are specified, then only undo elements
that apply to text between BEG and END are used; other undo elements
are ignored. If BEG and END are nil, all undo elements are used.