%%
%% The LaTeX Companion, 3ed
%%
%% Example 3-5-25 on page I-219 in "perpage --- Resetting counters on a \enquote {per-page} basis".
%%
%% Copyright (C) 2022 Frank Mittelbach
%%
%% It may be distributed and/or modified under the conditions
%% of the LaTeX Project Public License, either version 1.3c
%% of this license or (at your option) any later version.
%%
%% See https://www.latex-project.org/lppl.txt for details.
%%

\documentclass{tlc3exa}
\pagestyle{empty}
\setcounter{page}{6}
\setlength\textwidth{124.20126pt}
\setlength\textheight{5\baselineskip}
\newcounter{mnote} \renewcommand\themnote{\alph{mnote}}
\newcommand\mnote[1]{{\refstepcounter{mnote}%
  \marginpar[\small\raggedleft\textsuperscript{(\themnote)}\itshape #1]%
            {\small\raggedright\textsuperscript{(\themnote)}\itshape #1}}}
\usepackage{perpage} \MakePerPage{mnote}
\addtolength\textwidth{-38pt}
\setlength\marginparwidth{36pt}
\setlength\marginparsep{5pt}
\sloppy % because the examples are so small ...
%StartShownPreambleCommands
% code as above
%StopShownPreambleCommands

\begin{document}
Some text\mnote{First.} with a
footnote. More\footnote{Second
as footnote.} text. Even more
text.\mnote{Third!} And even
more\mnote {Fourth.} text.
Final text.\footnote{Fifth!}
\end{document}