Letterspacing (tracking) with fontspec

Question

As I'm reading the fontspec manual it seems like I should be able to loosen the tracking of a line of type like this:

\documentclass[border=1mm]{standalone}
\usepackage{fontspec}

\addfontfeature{LetterSpace=50.0}

\begin{document}

    Full fathom five thy father lies

\end{document}

but it doesn't work. What needs to change?

Answer 1

There's no font selection to add it to.

\RequirePackage{luatex85}
\documentclass[border=1mm]{standalone}
\usepackage{fontspec}

\begin{document}
\fontspec{Latin Modern Roman}

Full fathom five thy father lies

\addfontfeature{LetterSpace=50.0}
Full fathom five thy father lies

\end{document}

Obviously, you shouldn't use \fontspec in this way for a base font, but for the purpose of the example, it should suffice.