# “Rare” ligatures in LuaLaTeX and LMR font

How do I get "Rare/Discretionary" ligatures with the Latin Modern Roman Font in LuaLateX?

So far I have loaded the fontspec package and have tried several different approaches the most promising looking being: (from here)

\documentclass[10pt]{article}
\usepackage{fontspec}
\setmainfont[Ligatures=Rare,SmallCapsFont={Latin Modern Roman Caps}]{Latin Modern Roman}
\begin{document}
Unfortunately though, the Q of Queen still has a short tail, film however has the correct ligature.
\end{document}


I fear the answer may be: Use XeTeX. However I am using LuaLateX for drawing trees and therefore could not move to XeTeX without significant work. (As far as I am aware.)

• The Latin Modern fonts don't provide that feature. – egreg Feb 19 '16 at 21:49
• @egreg That explains the problem! For future reference where can I check this sort of thing for myself? – o.comp Feb 19 '16 at 22:01
• There's no general method, I'm afraid. The Latin Modern fonts do have the dlig feature, but I don't really know which ones it enables. – egreg Feb 19 '16 at 22:14
• Looking with FontForge, I see that the dlig table just implements the standard TeX ligatures. As far as I know Libertinus Serif has the long tailed Q (enabled by default). – egreg Feb 19 '16 at 22:24
• otfinfo -f <font file> will tell you which features a font file supports. However, it won't, on its own, tell you what exactly each feature does for that font, as @egreg points out. – cfr Feb 20 '16 at 0:11

For instance, Latin Modern Roman has a dlig feature, which is enabled in fontspec with Ligatures=Rare or Ligatures=Discretionary, but the relative subtable just shows that essentially the standard TeX ligatures are enabled (which is already done by the default Ligatures=TeX option.
The picture shows a screen shot of how I looked at the subtable responsible for the dlig feature.