Only recently have I learnt to distinguish inline from display-style maths mode by using \mode_if_inner:TF. It would be helpful for those of us who come to expl3 programming without a good prior grounding in TeX if a comment to this effect could be added to the documentation (interface3.pdf). Andrew --- This email has been checked for viruses by Avast antivirus software. https://www.avast.com/antivirus