help doc says, the variable can contain a list (or) number (or) minus symbol. I mostly set a number as the
prefix-arg by keypress,
I ask this, since
(defun isearch-forward (&optional regexp-p no-recursive-edit) (interactive "P/np") (........))
takes the search string through interactive key "P" but i am having zero clue on how to set a string to this prefix-arg?