On 2013–09–30 Hans Hagen wrote:

> these are unrelated mechanisms where the first one just does some
> pdf magic ... no feedback to tex about widths (ok, i could write
> something better but never had and still don't have a reason for
> that kind of low level pdf based approach to be really deeply
> integrated)

Thanks for the explanation. I was looking for a way to do slight
letter spacing without breaking ligatures and thought I could
leverage the stretch effect for that.

Marco