Drew, thanks for the answer. Unfortunately I need a different behavior in
my particular case. I was proposed with similar work-around also on stack
overflow. Though, I'm often using incremental search for query specific
tags in a large text file which is used like database system with help of
some configuration and scripts. Before each incremental search there is a
macro which places me to BOF and afterwards starts incremental search. For
this scheme it would be very convenient just not to append mismatched part
at all. I understand that it's not that standard feature and I use
different approach when let's say coding or typing text but again for this
particular case I need the mentioned behavior. It will save me some
additional clicks to backspace and/or c-s  c-g. In other words: I'm
looking for a way of not showing mismatched characters during incremental
search. Thanks a lot for your time.

On Thu, Dec 13, 2012 at 2:14 AM, Drew Adams <drew.adams@oracle.com> wrote:

> > How can I [get] this behaviour:
> >  Start incremental search and search for "keyz"
> >  "key" is displayed in the search echo area and the "key"
> >  part in "keywords" is higlighted
> >  Press s
> >  "keys" is found and highlited
>
> I don't have an answer for you, but the suggestion is an interesting one.
>
> A variant that could be useful (which I also don't have a recipe for):
>
> Type `keyz'.
> The `z' is highlighted as a mismatch (this is already available).
> Hit a key to delete the mismatched part (in this case, just `z'.
> Type `s' and continue.
>
> When I introduced highlighting of the mismatch part, I took it from Icicles
> highlighting of completion input mismatch.  There, you can hit `C-l' twice
> to
> remove the mismatched part.  (The first `C-l' just moves the cursor to the
> mismatch beginning, so you can insert there.)
>
> In Isearch there is no equivalent - no key that removes the mismatched
> part.
> Maybe I'll add that possibility.  What you can do is hit `M-e', which puts
> you
> in editing mode and moves the cursor to the mismatch beginning.  Then hit
> `C-k'
> to kill the mismatch portion, then `C-s' to resume searching.  So `M-e C-k
> C-s'.
>
>