[NTG-context] How to clone \underbar?

Dear list, how can I clone \underbar (for the purpose of changing settings for the clone afterwards)? Just using \definebar to inherit \underbar’s properties does not entirely work, see MWE: \definebar[myBar][underbar] \starttext underbar text mode: \underbar{$a^b$} \crlf underbar math mode: $\underbar{a^b}$ \crlf myBar text mode: \myBar{$a^b$} \crlf myBar math mode: $\myBar{a^b}$ \stoptext Thanks and best regards, Florian