isearch-allow-prefix

isearch-allow-prefix is a variable defined in `isearch.el'.
Its value is

t

Documentation:
Whether prefix arguments are allowed during incremental search.
If non-nil, entering a prefix argument will not terminate the
search. This option is ignored (presumed t) when
`isearch-allow-scroll' is set.

You can customize this variable.

This variable was introduced, or its default value was changed, in version 24.4 of Emacs.