Nice!

> > +(add-to-list 'completion-styles-alist
> > +             '(external-completion-style
>
> This sounds a bit like the RAS syndrome, just without the acronym.
> Why not use just `external`?

Good idea. Done.

> > +(defun external-completion-table (lookup
> > +                                 category &optional metadata
> > +                                 try-completion-function)
>
> Ah, I see you made tryc optional :-)
> I'd put `category` on the first line, tho.
> If you don't like the resulting indentation of the second line, then
> just add a space before "lookup" :-).

Haha.  Yes I fixed it.  And category is now the first argument, I think it's

slightly more logical.

> > +TRY-COMPLETION-FUNCTION is an poorly understood implementation detail.
>
> Not at all.  It's a functionality that only makes sense for some UIs
> (not those based on the idea of selecting among a set of choices), and
> it tends to work better with more "primitive" completion styles (it
> asymptotically becomes useless the harder the completion style tries to
> find completions).

I'm still confused, I need examples to understand this stuff, and I'm afraid

If I do I'll forget all about it next time around. But personally I don't _have_ to 

understand it, really.  Been using this for years successfully without 

understanding it, so why should I start now? I made the docstring 

even more cheeky so you can see what I mean.

> AFAICT the `external-completion-tryc/allc` symbols are not exposed to
> users of this library any more so we could use ones with a double hyphen.

Good idea. Done.