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