>> A suggestion:
>>
>> (kbd-valid-p "<mouse-1>")
>> (kbd-valid-p "<Scroll_Lock>")
>>
>> should return t, and
>
> Good point.  This does make one of the syntax checks either less 
> effective, or the syntax is ambiguous.  I went with the latter, but I'm 
> not sure that's the right thing to do here.
>
> The kbd syntax is
>
> "C-M-<return>"
>
> but allowing dashes inside the brackets means that
>
> "<C-M-return>"
>
> should be parsed as the key named "C-M-return" (which isn't really 
> possible).
>
> So I just added some special-casing to disallow the "<C-M-return>" form 
> in kbd-valid-p.  We'll see...
>
>> (kbd-valid-p "<123>")
>>
>> should (I think) return nil.  IOW, kbd-valid-p should use:
>
> I'm not sure -- can there be keys named "123"?  I don't know what the 
> rules are here -- is there an authoritative source for the syntax of 
> these names somewhere?
>

This is no different from "C-M-return" which you disallow.  In theory 
there could be a key or event whose symbolic name is "C-M-return".  In 
theory there could be a key or event whose symbolic name is "123" (or even 
"0", which is different from the key "0").  In theory there could also be 
a key or event whose symbolic name is "ü", IOW, <ü>.

If the point is to introduce a strict syntax, I think it's up to you to 
decide which key and event names are okay from the point of view of Emacs. 
I think the following should be okay:

- contains at least two characters
- starts with an ASCII letter
- is followed by ASCII letters, digits, - or _
- each - must be preceded by at least two letters or digits
- ends with an ASCII letter or digit

Of course this is rather complex to put in a regexp, which is one of the 
reasons I chose to use a C function to do that check.