In the allrunes.sty documentation (which uses Metafont), I’ve recently seen the \textlf macro for the first time. It selects a light font and therefore accompanies the frequent command \textbf and its sibling \textmd for default ‘medium’.
Searching for ‘textlf’ on SX showed that this string is also a package option for Minion Pro, but there it switches on lining figures and it seems some other packages have a command \textlf that does the same.
- So I wonder, how commonly supported is
\textlfand is there an established alternative without conflicts? - More generally, if I’m using a typeface with fonts for many weights available (e.g. thin, light, semi-bold, bold, heavy, black …), how are they best accessed in Xe-/LuaTeX?
The second question is relevant, for instance, if I was to write a supporting package for an Open Type typeface that provided predefined \text… macros, which wrap fontspec’s \newfontfamily or rather the less known \newfontface within \DeclareTextFontCommand.

\textlt– Crissov Jul 09 '14 at 20:44\textlg, I think. But I don't think there is a real standard here. – cfr Jul 09 '14 at 23:40