Can one kern math font euler.otf using lualatex and fontspec?

Question

I am at it again... :)

Using the http://github.com/khaledhosny/euler-otf/blob/master/euler.otf font, can one kern distance between T and P with Lualatex?

Clearly, my attempt does not work...

Could it perhaps be that the used glyphs are not called T and P?

\documentclass{standalone}
\usepackage{filecontents}

\begin{filecontents*}{mykern.fea}
languagesystem DFLT dflt;
languagesystem latn dflt;
feature kern {
    pos T P 200;
} kern;
\end{filecontents*}

\usepackage{fontspec}
\usepackage{unicode-math}
\setmathfont[math-style=upright,FeatureFile=mykern.fea]{euler.otf}

\usepackage{microtype}
\usepackage{siunitx}

\begin{document}

$TP$

\end{document}

Answer 1

Not a full answer, but too long for a comment and I hope this is a useful start.

The lualatex version of unicode-math loads maths fonts with Renderer=Basic and so turns off such features.

\documentclass{article}
\usepackage{filecontents}

\begin{filecontents*}{mykern.fea}
languagesystem DFLT dflt;
languagesystem latn dflt;
feature kern {
    pos T P 200;
} kern;
\end{filecontents*}

\usepackage{fontspec}
\usepackage{unicode-math}
\setmathfont[math-style=upright,FeatureFile=mykern.fea]{euler.otf}

\usepackage{microtype}
\usepackage{siunitx}

\begin{document}

\fontspec[FeatureFile=mykern.fea]{euler.otf}
TP

\fontspec[Renderer=Basic,FeatureFile=mykern.fea]{euler.otf}
TP

$TP$

\end{document}

You should also note that in maths the font is loaded with Script=Math.