\begin{note} and \end{note} should be \enternote and \exitnote

[timsong-cpp]

There are a couple instances in templates.tex.

[jwakely]

It might be better to merge the note environment from the IS, as introduced by cplusplus/draft#238

I did this for the Networking TS, see cplusplus/networking-ts@f1fa7f3#diff-c73e563e3285ee05f74a4d067d00b52c