RE: feature/completions-highlight-modifications e3c5b99 3/6: Add completions-highlight-mode initial implementation.

[Drew Adams <drew.adams@oracle.com>]

> > Icicles uses `C-insert' to move the cursor back and
> > forth between the minibuffer and *Completions*.  It
> > moves between the current candidate in the minibuffer
> > (from cycling) to/from the same candidate in
> > *Completions*.
> 
> What the default completions implementation is still missing
> is a command/key to insert the selected completion
> from the the *Completions* buffer to the minibuffer
> without exiting the minibuffer.

Does it have a key that moves from a completion candidate
in the minibuffer (e.g. from cycling) to the same candidate
in *Completions*?  That's also missing, AFAIK, in addition
to placing the current completion in the minibuffer as you
cycle.  No?

The same key should be used for both operations: minibuffer
to *Completions* and *Completions* to minibuffer.  And it
should go to the "current" completion candidate in each case.

And it should be a key that's not ordinarily used for editing,
if it's made available in the minibuffer.  For example, we
shouldn't use a key such as `insert'.
___

It's already the case that perfectly fine self-inserting keys
(`?', `SPC') have been excluded, in the minibuffer, from their
ordinary behavior (self-inserting).

That was misguided, IMO.  It took us decades to finally get
`SPC' to be self-inserting, and even then, it's only for
`read-file-name', not `completing-read'.  Why it was assumed
that completion candidates would/should not contain space
chars or question marks, I don't know.