% This file is public domain
 % If you want to use arara, you need the following directive:
 % arara: pdflatex: { synctex: on }
\documentclass{article}

\usepackage{mfirstuc-english}

\begin{document}

\makefirstuc{abc}.

\makefirstuc{{\em abc}}.

\makefirstuc{\emph{abc}}.

\makefirstuc{\ae bc}.

\makefirstuc{{\ae}bc}.

\newcommand{\abc}{abc}%
\xmakefirstuc{\abc}.

\capitalisewords{the wind in the willows}

\capitalisewords{a book of rhyme.}

\MFUclear

\capitalisewords{the wind in the willows}

\capitalisewords{a book of rhyme.}

\capitalisewords{a book\space of rhyme.}

\newcommand{\mytitle}{a book\space of rhyme.}
\capitalisewords{\mytitle}

\xcapitalisewords{\mytitle}

\end{document}