\documentclass{book}
\usepackage{ulem}
\usepackage{lipsum}
\usepackage{stackengine}
\usepackage[dvipsnames, svgnames, x11names, table]{xcolor}
\newcommand{\emone}[1]{\textcolor{RoyalBlue3}{\stackunder{\uline{#1}}{\scriptsize M1}}}
\begin{document}
\emone{this is a text this is a text this is a text this is a text this is a text this is a text this is a text this is a textthis is a text this is a text this is a text}
\end{document}
I am trying to put some text underline. I made breakable underlined text by some package and for the text under it I used stackengine package but it is a hbox type so it is not possible to break it in multi line. So pls share with me your comment on this pic and give your solutions.

\emones just put on its own (like in a math display)? – Werner Dec 17 '20 at 20:52cont NPinstead ofNP, say). Is there anything that would prevent you from doing it manually? – Werner Dec 17 '20 at 22:10