[XeTeX] stacking diacritics without mark-to-mark

[maxwell]

On 2014-03-12 14:47, Joshua and Amy wrote:
> I'm typesetting with XeLaTeX, using fontspec, and calling a font
> provided to me by the publisher of a manuscript I'm working on. (Same
> as my previous post!)
> 
> The language I work with has a letter O with circumflex and breve
> (U+00F4,U+0306): ô̆. However, the publisher-provided font does not
> use mark-to-mark positioning, so when I typeset in XeLaTeX, the
> combining breve overlays the circumflex.
> 
> Back in January of 2013, there was discussion of this very issue,
> which included talk of a potentially forthcoming solution where XeTeX
> would handle this problem for us. Does anyone know whether there is
> now a straightforward way of doing this?

I'm the one who started the thread a year ago, and I'm very definitely 
interested in this problem.  The post saying that this problem would 
soon be fixed is this one:
    http://tug.org/pipermail/xetex/2013-January/024031.html
namely
    ...next XeTeX (thanks the new HarfBuzz layout engine),
    will try to position the accents using their bounding boxes
    if the font does not have a GPOS table, so it should produce
    better results in this case (unless the font in question
    does have a GPOS table).

    Regards,
    Khaled
Afaict, this does not work under the TeXLive 2013 version, at least not 
with this publisher's font.  Am I missing s.t.?

    Mike Maxwell