% !TEX TS-program = lualatex
\documentclass{article}

\usepackage[autocompile]{gregoriotex}

\begin{document}

\gabcsnippet{(c4) <c> Nar(c)ra(egf)bo(f.) </c> (::)  }

\gabcsnippet{(c4) <c> Nar(c)ra(egf){bo}(f.) </c> (::) }

\end{document}