Add space between margin and footnote marker

Question

Consider the following minimal working example:

\documentclass{amsart}
\usepackage[hang]{footmisc}
\setlength{\footnotemargin}{1em}

\begin{document}
Content.\footnote{Footnote}
\end{document}

I want to add a small space (say, 1 em) between the margin and the footnote marker while leaving everything else unchanged.

Answer 1

\footnotemargin has a different meaning when using hang. From the footmisc documentation (section 1.11 Option hang, p 4):

This option sets the footnote mark flush with the margin, and makes the body of the footnote hang at an indentation of \footnotemargin (if that is a positive distance), or the width of the marker (if \footnotemargin <= 0). The option code itself leaves \footnotemargin at its default value of 1.8em.

To add some space before the footnote marker, patch \@makefntext using etoolbox:

\documentclass{amsart}
\usepackage[hang]{footmisc}
\usepackage{etoolbox}
\makeatletter
\patchcmd{\@makefntext}{\llap}{\quad\llap}{}{}
\makeatother
\setlength{\footnotemargin}{2em}
\setlength{\textheight}{5\baselineskip}% Just for this example
\begin{document}
Content.\footnote{Footnote}
\end{document}

The above patch inserts \quad (or, technically, \hskip1em\relax) before the first \llap - used to place the marker after measuring its width.