On 2013-10-04 21:57 +0800, Stefan Monnier wrote:
[snipped 3 lines]
> I like the idea of displaying the available choices, but I'm not sure
> "0.5s delay" is a good enough trigger: it's probably a fine choice for
> some users, but usually Emacs doesn't like to use such time-dependent
> behavior too much.
>
> Could we offer, additionally to the delay, a different trigger
> (e.g. help-char and help-event-list)?
>
>
>         Stefan

Good idea. The attached patch implements this. i.e. if one sets
register-preview-delay to t it means forever, i.e. the timer is never
set. Users can customise register-read-help-char to nil if they don't
want any help-char to bring up the preview window.

BTW, the delay is so that if you can remember which register to choose
within some time (0.5s) you shall never see the preview window.

[snipped 10 lines]
>> PS: How does it compare to register-list?  Could they be
>> consolidated?
>
> I hope so.  The Org merge is higher on my todo-list, but working on
> register-list.el comes right after.

I leave a hook i.e. register-preview-functions for customising how the
preview should be presented. I am not sure other ways to have
integration with register-list. Comments welcome.

Best wishes,
Leo