Writing text in parallel, in twosided mode

Question

Use case: I'd like to write a two-sided document, with prose on the RHS and sidenotes on the LHS, with (if possible) the note appearing parallel aligned with its label in the prose.

I can do this with the paracols package, with all the text on one page. But I don't know how to lay it out across two pages.

Approximate MWE:

\documentclass[a4paper]{article}
\usepackage[landscape]{geometry}
\usepackage{paracol}
\usepackage{lipsum}

\begin{document}
\begin{paracol}{2}
\switchcolumn
  \lipsum[1]
\switchcolumn*
  \textbf{prose}: The long and boring part of a document.
\switchcolumn
This constitutes a long and verbose set of \textbf{prose}.
\switchcolumn*
\switchcolumn
\lipsum[1]
\switchcolumn*
\switchcolumn

\end{paracol}
\end{document}

So, as you can see, for each reference on the recto page (at the moment just regular bold text), I'd like to add details on the corresponding line on the verso page. Is there a way to refer to the "corresponding line on the opposite page"? There are various edge cases like "what if you have two references on the same line" or "what if it doesn't fit on the page" but I imagine these are not hard to deal with.

Answer 1

I still don't have a strong grip with regards to what you really expect. Here is what I have come up with. Use todonotes and place your definition on the left of the page (by putting \reversemarginpar in the preamble or \normalmarginpar if you would like to put them on the right). Having two notes close to each other isn't a problem. The only problem is having long note that spans beyond the bottom margin or even the whole paper. The only fix I can think of is the use the \newpage every time you encounter such thing.

\documentclass[a4paper]{article}
\usepackage[backgroundcolor = none,
            %linecolor= none,                   % Removes the line
            %bordercolor= none,                 % Removes the border
            bordercolor=red]{todonotes}
\usepackage[landscape]{geometry}
\usepackage{xcolor}
\usepackage{lipsum}


% Can change the width of the note
\geometry{lmargin = 2in, marginparwidth = 1in}  % lmargin should be +1 inch larger than marginparwidth

%\normalmarginpar                               % Used to place the marign on the right side.
\reversemarginpar                               % Used to place the marign on the left side.
\begin{document}
\lipsum[1]. Now I will add a note here \todo{First note has been added!}.
Here is the second note: \todo{Second note is added, note (pun intended) that both 
notes are very close and \textit{should} overlap but this has been taken care of.}
\lipsum[2-4] A third note has been added.\todo{Third note is added here!!} 
Now, continue to the next paragraph.\lipsum[5] 
\todo{Third note is added and it needs to be very very very very very very very 
very very very very very very very very very very very very very very very very 
very very very very very very very very very very very very very very long}\lipsum[6]
\end{document}

If you use \newpage before inserting the note i.e.

... Now, continue to the next paragraph.\newpage \lipsum[5] \todo{Third note is added and it needs to be very very very very very very very very very very very very very very very very very very very very very very very very very very very very very very very very very very very very very long}\lipsum[6]

you will have to following: