This is my little MWE,
\documentclass{book}
\usepackage{blindtext}
\usepackage{geometry}
\geometry{
includemp, % or include something else?
paper=a4paper,
marginparwidth=45mm
}
\begin{document}
Of course \marginpar{\blindtext[7]} \blindtext[7]
\end{document}
And the output is,
Why dummy text in the marginal note doesn't continue to next pages?
I'm entering this as a different answer since it is based on \vsplit and has none of the drawbacks of the paracol approach. Note that it takes two runs to compute the distance to the bottom of the text area.
\marginflow is used instead of \marginpar. \marginrepeat is only used in \afterpage.
Interestingly, without all the \newpages this will only go for 3 pages.
\documentclass{book}
\usepackage[showframe]{geometry}
\geometry{
includemp, % or include something else?
paper=a4paper,
marginparwidth=45mm
}
\usepackage{afterpage}
\usepackage{tikzpagenodes}
\newlength{\bottom}
\newsavebox{\marginparbox}
\newcommand{\marginflow}[1]% #1 = text
{\strut\tikz[remember picture,overlay]% compute distance to bottom of text area
{\pgfextracty{\bottom}{\pgfpointdiff{\pgfpointanchor{current page text area}{south}}{\pgfpointorigin}}%
\global\bottom=\bottom}%
\advance\bottom by 0.4\baselineskip
\parbox{\marginparwidth}{\global\setbox\marginparbox=\vbox{#1}}%
\ifdim\bottom>\dimexpr\ht\marginparbox+\dp\marginparbox\relax
\marginpar{\raisebox{\dimexpr 0.6\baselineskip-\height}{\usebox{\marginparbox}}}%
\else
\setbox1=\vsplit\marginparbox to \bottom
\marginpar{\raisebox{\dimexpr 0.6\baselineskip-\height}{\usebox1}}%
\ifdim\ht\marginparbox>-\dp\marginparbox
\afterpage{\marginrepeat}%
\fi
\fi\ignorespaces}
\newcommand{\marginrepeat}{\vspace*{-\baselineskip}%
\ifdim\textheight>\dimexpr\ht\marginparbox+\dp\marginparbox\relax
\marginpar{\raisebox{\dimexpr 0.6\baselineskip-\height}{\usebox{\marginparbox}}}%
\else
\setbox1=\vsplit\marginparbox to \textheight
\marginpar{\raisebox{\dimexpr 0.6\baselineskip-\height}{\usebox1}}%
\ifdim\ht\marginparbox>-\dp\marginparbox
\afterpage{\marginrepeat}%
\fi
\fi}
\usepackage{blindtext}
\begin{document}
So here I am going on and on about absolutely nothing when I happen to mention something which I want to
describe in the margins HERE \marginflow{\blindtext[7]} then continue as if nothing had happened.
\null\newpage
\null\newpage
\null\newpage
\null\newpage
\null\newpage
\end{document}
The drawback with this solution is that you can't just insert the "note" into the middle of a sentence or paragraph.
\documentclass{book}
\usepackage[showframe]{geometry}
\geometry{
includemp, % or include something else?
paper=a4paper,
textwidth=418.25368pt,% \the\dimexpr \textwidth+\marginparsep+\marginparwidth\relax
marginparsep=0pt,
marginparwidth=0pt
}
\usepackage{paracol}
\setcolumnwidth{\dimexpr \textwidth-45mm-\columnsep\relax,45mm}
\twosided
\usepackage{blindtext}
\begin{document}
\begin{paracol}{2}
Of course
\switchcolumn*\blindtext[7]\switchcolumn
as I was saying
\end{paracol}
\end{document}
This uses \everypar to perform the switch at the beginning of the paragraph (with a vertical offset). It takes two runs, since the information from \marginpar is stored in the aux file. The limit is only one \marginpar per paragraph.
\documentclass{book}
\usepackage[showframe]{geometry}
\geometry{
includemp, % or include something else?
paper=a4paper,
textwidth=418.25368pt,% \the\dimexpr \textwidth+\marginparsep+\marginparwidth\relax
marginparsep=0pt,
marginparwidth=0pt
}
\usepackage{paracol}
\setcolumnwidth{\dimexpr \textwidth-45mm-\columnsep\relax,45mm}
\twosided
\makeatletter
\newcounter{absparagraph}
\newlength{\marginpar@offset}
\newif\ifmarginpar
\newif\ifrepeatpar
\newcommand{\newparagraph}[2]% #1 = pragraph, #2 = y location
{\expandafter\gdef\csname paragraph@#1\endcsname{#2}}
\newcommand{\newmarginpar}[3]% #1 = pragraph, #2 = y location, #3 = text
{\expandafter\gdef\csname marginpar@y@#1\endcsname{#2}%
\expandafter\gdef\csname marginpar@text@#1\endcsname{#3}}
\renewcommand{\marginpar}[1]% #1=text
{\pdfsavepos
\protected@write\@auxout{}{\string\newmarginpar{\theabs@paragraph}%
{\noexpand\number\pdflastypos}{#1}}\ignorespaces}%
\newcommand{\AtBeginParagraph}{\ifmarginpar\else
\ifrepeatpar\repeatparfalse
\else
\stepcounter{absparagraph}%
\xdef\theabs@paragraph{\theabsparagraph}%
\strut\pdfsavepos
\protected@write\@auxout{}{\string\newparagraph{\theabs@paragraph}%
{\noexpand\number\pdflastypos}}%
\@ifundefined{paragraph@\theabs@paragraph}{}{%
\@ifundefined{marginpar@text@\theabs@paragraph}{}{%
\global\marginpar@offset=\csname paragraph@\theabs@paragraph\endcsname sp\relax
\global\advance\marginpar@offset by -\csname marginpar@y@\theabs@paragraph\endcsname sp\relax
\vspace{-\baselineskip}%
\marginpartrue
\switchcolumn*
\vspace*{\marginpar@offset}\csname marginpar@text@\theabs@paragraph\endcsname
\switchcolumn
\marginparfalse\repeatpartrue}}%
\fi
\fi}
\makeatother
\AtBeginDocument{\everypar{\AtBeginParagraph}}
\usepackage{blindtext}
\begin{document}
\begin{paracol}{2}
So here I am going on and on about absolutely nothing when I happen do mention somtehing to which I want to
describe in the margins HERE \marginpar{\blindtext[7]} then continue as if nothing had happened.
\end{paracol}
\end{document}