20.1.8 Scrolling During Incremental Search

You can enable the use of vertical scrolling during incremental search (without exiting the search) by setting the customizable variable isearch-allow-scroll to a non-nil value. This applies to using the vertical scroll-bar and to certain keyboard commands such as <PRIOR> (scroll-down), <NEXT> (scroll-up) and C-l (recenter). You must run these commands via their key sequences to stay in the search—typing M-x will terminate the search. You can give prefix arguments to these commands in the usual way.

This feature won't let you scroll the current match out of visibility, however.

The feature also affects some other commands, such as C-x 2 (split-window-vertically) and C-x ^ (enlarge-window) which don't exactly scroll but do affect where the text appears on the screen. In general, it applies to any command whose name has a non-nil isearch-scroll property. So you can control which commands are affected by changing these properties.

For example, to make C-h l usable within an incremental search in all future Emacs sessions, use C-h c to find what command it runs. (You type C-h c C-h l; it says view-lossage.) Then you can put the following line in your ‘.emacs’ file (see section The Init File, ‘~/.emacs’):

(put 'view-lossage 'isearch-scroll t)

This feature can be applied to any command that doesn't permanently change point, the buffer contents, the match data, the current buffer, or the selected window and frame. The command must not itself attempt an incremental search.