[luatex] sub and superscripts in Lua(La)TeX with tfm/otf

[Arno Trautmann]

Hi all,

I encountered some strange behaviour regarding the subscript and 
superscripts in LuaLaTeX compared to pdfLaTeX. Consider the following 
small example:

%\RequirePackage{luatex85}
\documentclass{scrartcl}
%\usepackage{subdepth}
%\usepackage{unicode-math}

\begin{document}
\[a_ia_i^+a^+a_i^\dagger\]
\[M_n M_n^\dagger M_n^+\]
\end{document}

Compilation with pdfLaTeX results in shifted positions for the sub and 
super scripts according to the TeXbook. The package subdepth equalizes 
them, which in this case looks nicer.
With LuaLaTeX, the subdepth package does not work, and has no effect on 
the positioning whatsoever. David suggested to ask for a reason for this 
behaviour on the luatex-list.
Making things more complicated: If I load unicode-math and thus 
lm-math.otf, the subdepth package still has no effect. BUT: The 
positions of the subscrips is plain wrong in my opinion in the second 
line, as in M_n^\dagger the subscript is placed *higher* than in the 
other cases. Which does not happen for the a_i^\dagger.

In total, I see a lot of different placements of the sub/superscripts 
and I am a bit lost which one is the right one, which one might be a bug 
and which one is intendedly different – the placement depends on the 
engine, the font, the size of the nucleus and the size of the 
superscript. Can anybody help me figure this one out?
(What I *want* is the behaviour of pdfLaTeX + subdepth to work in 
LuaLaTeX + unicode-math)

Best,
Arno