[...]
> Why?
> Because there have been several questions on #zsh{,.de} on how to get
> events from the history with the date included a command was invoked.
> Because bash seems to have a command for this. But I don't remember it.

Bash has this? Never heard of that. Nor would I care.
I'm not against this function at all, I'd just never use it.

This obviously requires extended_history, which grml enables by
default, so that should not be an issue.

[...]
> +  whatwhen()  {
[...]
> +            einfo ${usage} ; /bin/false ; eend $?

Personally, I dislike using these e*() function for anything else but
system scripts. For shell functions (which basically work a lot like
usual programs/commands) I'd prefer plain output a lot.

[...]
> +            fc -lE -m "*[${(L)1[1]}${(U)1[1]}]${1[2,-1]}*" ${2:-\-100} $3
[...]

Would you mind explaining this one a bit?
I'm not exactly familiar with the 'fc' builtin.

Also, I would assign $1 etc. to named variables, which would increase
readability.

Regards, Frank