\input luaotfload.sty

% https://bugs.freedesktop.org/attachment.cgi?id=72363
\font\testa=file:TestLig.ttf:script=tibt;+ccmp+abvs+blws+kern at 10pt

\testa གཚོའི་ཁིའུ་ཨཱཿཀ

% good result for the first part: 
% https://bugs.freedesktop.org/attachment.cgi?id=72365
% for the second part, the two circles shoud appear clearlybefore the last 
% letter, not mixed with it

% see http://lists.freedesktop.org/archives/harfbuzz/2013-April/003101.html
% for some technical details.

\bye