Thank you Joseph and Frank for your help and explanations which were really useful to me. Inspired by your replies, I have found many useful links on SE, packsges in TeXLive, and references to read about expl3 and LaTeX3, including: https://tex.stackexchange.com/search?q=expl3 https://tex.stackexchange.com/search?q=\ExplSyntaxOn https://tex.stackexchange.com/questions/tagged/latex3 https://www.texdev.net/2014/02/02/programming-latex3-a-summary-so-far/ fontspec, siunitx, spath3, unicode-math packages in l3packages directory packages in l3experimental directory Thanks, Tisha