How to combine nested footnotes with memoir?

Question

I want to implement the nested footnotes appearing in a single sequence as in Nested footnotes with the memoir class. While the solution given by Werner as an answer to that question does work at first glance, but because it is based on the definitions in the article class it eliminates the multiple footnote feature in memoir (similar to \usepackage[multiple]{footmisc}). The mwe below shows the problem. The correct formatting of the footnote marks can be seen by commenting out the redefinitions of \footnotemark and \footnotetext.

\documentclass{memoir}

\usepackage{letltxmacro}

\newcounter{fnmarkcntr}
\newcounter{fntextcntr}
\makeatletter
\renewcommand{\footnotemark}{%
   \@ifnextchar[\@xfootnotemark
     {\stepcounter{fnmarkcntr}%
      \refstepcounter{footnote}\label{footnotemark\thefnmarkcntr}%
      \protected@xdef\@thefnmark{\thefootnote}%
      \@footnotemark}}
\makeatother
\LetLtxMacro{\oldfootnotetext}{\footnotetext}
\renewcommand{\footnotetext}[1]{%
  \refstepcounter{fntextcntr}
  \oldfootnotetext[\ref{footnotemark\thefntextcntr}]{#1}
}

\begin{document}

This text has footnotes%
\footnote{Which contains sub-footnotes\footnotemark% \multfootsep
\footnotemark that should be marked clearly as separate}%
\footnotetext{This footnote should be labeled `2'}%
\footnotetext{This footnote should be labeled `3'}%
\footnote{Another footnote}%

\end{document}

The output has badly formatted footnote marks, both in the main text and in the first footnote:

Without the two \renewcommands we get the default output which numbers the footnotes wrong:

I think \m@makefootnotemark (and maybe other macros) from memoir needs to be modified but its definition (and usage) is too complicated for me to figure out the necessary change by analogy.

Answer 1

I am not sure if this is reason. I think the \label command introduce space to mess up the multifootnote typing. This is a working example:

\documentclass{memoir}
\newcounter{myfn}
\newcounter{tpmyfn}
\makeatletter
\def\footnotemark{\@ifnextchar [\@xfootnotemark%
{\advance\c@myfn1\c@tpmyfn\numexpr\value{myfn}+\value{footnote}%
\protected@xdef\@thefnmark{\thetpmyfn}%
\@footnotemark}}
      
\def\footnotetext{%
     \@ifnextchar [\@xfootnotenext%
     {\stepcounter{footnote}\c@myfn0\protected@xdef\@thefnmark{\thempfn}%
    \@footnotetext}}
\makeatother
\begin{document}

This text has footnotes%
\footnote{Which contains sub-footnotes\footnotemark\footnotemark that should be marked clearly as separate}%
\footnotetext{This footnote should be labeled `2'}%
\footnotetext{This footnote should be labeled `3'}%
\footnote{Another footnote}%
\end{document}