Author Footnote Indentation

Question

How do you set the footnote margin for footnotes included in \title, \author, or \date?

\documentclass[11pt, a4paper]{article}
    \usepackage[hang, flushmargin]{footmisc}
    \title{Title}
    \author{Author\footnote{Indentation is incorrect.}}
    \setlength{\footnotemargin}{15pt}
\begin{document}

\maketitle

Hello world.\footnote{Indentation is correct.}
    
\end{document}

In the above example, \setlength{\footnotemargin}{15pt} only changes the indentation of the footnotes in the body of the document.

Answer 1

\maketitle as defined by the article class redefines \@makefntext. This means that inside \maketitle footmisc's definition of \@makefntext is forgotten…

You can patch \maketitle and change the definition back again:

\documentclass[11pt, a4paper]{article}
\usepackage[hang, flushmargin]{footmisc}
\setlength{\footnotemargin}{15pt}

\title{Title}
\author{Author\thanks{Indentation is incorrect.}}

\usepackage{etoolbox}
\makeatletter
\let\fm@makefntext\@makefntext
\patchcmd\maketitle{\if@twocolumn}{\let\@makefntext\fm@makefntext\if@twocolumn}{}{\fail}
\makeatother

\begin{document}

\maketitle

Hello world.\footnote{Indentation is correct.}
    
\end{document}