Cfrgtkky

Edit: I am not happy with the 3 answers my first, smaller bounty got me. So I rewrote the question to set clear rules and a proper bounty.

The solution should create two environments, originalemail and response with the following effects:

• Text in the originalemail is typeset in a way that slightly (4pt) indents all text and adds a vertical line on the left.


• The response environment can only be used inside the environment and results in the vertical line being broken and the text being aligned on the left without the originalemails indentation. What is more, the response has to be aligned to the same margin on the left, irrespective of where in the originalemail it is placed (e.g., be within a (nested) itemize or enumerate).

Summary

• leave the layout of the original email in-tact (it should be possible to use sections, lists, paragraphs, floats, etc. as if it as was a plain TeX document and there were no responses and the numbering should be the same with and without respones)


• using these environments should require no editing of the code outside the response environment. In particular any suspension or resume of enumerate or itemize environments, if required by the solution should be automatic.


• The only way in which the original layout should change is that it show vertical line (2pt) on the left margin and ideally a slight indentation (4pt).


• responses and the fragments of the original email have to break pages as normal. (if you use parbox for the responses they wont)


• allow to insert replys anywhere in the the original text


• bonus if the solution is nesteable (i.e. the outer originalemail contains an older originalemail and responses)

Rules: for the bounty, you're free to build on the existing answers, i.e. @marmot's/Gonzalo Medina's TikZ approach to draw the line in the left margin, @Vinccool96's tcolorbox or my own rudimentary approach to automatically suspending and resuming lists.

Screenshot from Gmail that roughly summarizes what I need:

documentclass{article}



usepackage[most]{tcolorbox}

tcbuselibrary{breakable}

tcbuselibrary{skins}



newtcolorbox{emailstart}[3]{%

    standard jigsaw,

    opacityframe=0,

    opacityback=0,

    colback=transparent,

    grow to left by=-1.5em,

    boxrule=0pt,

    boxsep=0pt,

    breakable,

    enhanced jigsaw,

    title={On #2, #3 wrotepar},

    coltitle={black},

    attach title to upper={},

    borderline west={4pt}{0pt}{black},

    overlay unbroken and first={draw[shorten >=1.4pt, shorten <=1.4pt] ([yshift=-1.5em]frame.north west) -- ([yshift=-1.5em]frame.north east);},

    #1,

}



newtcolorbox{emailresume}[1]{%

    standard jigsaw,

    opacityframe=0,

    opacityback=0,

    colback=transparent,

    grow to left by=-1.5em,

    boxrule=0pt,

    boxsep=0pt,

    breakable,

    enhanced jigsaw,

    borderline west={4pt}{0pt}{black},

    #1,

}



newcounter{enumicounter} %counter that will save the enumeration counter



begin{document}

    begin{emailstart}{2019}{Einstein}

        begin{emailstart}{2018}{Sheß}

            Text Text Text Text



            Text Text Text Text Text Text Text

        end{emailstart}

        Here I am putting my answer text 

    end{emailstart}

    Oh, now I see your point





    begin{emailresume}

        begin{emailresume}

            section{A section}

            Some content a list

            begin{enumerate}

                item One

                setcounter{enumicounter}{value{enumi}} % save the enumeration counter

            end{enumerate}

        end{emailresume}

        Here even more, there's no indentation, because you closed the enumaration and the email

    end{emailresume}

    This is an answer to your answer

    begin{emailresume}

        begin{emailresume}

            begin{enumerate}

                setcounter{enumi}{value{enumicounter}} % continue the enumeration

                item Two

                setcounter{enumicounter}{value{enumi}} %save the enumeration counter

            end{enumerate}

        end{emailresume}

        Answer

        begin{emailresume}

            begin{enumerate}

                setcounter{enumi}{value{enumicounter}} % continue the enumeration

                item Three

                item Four

                setcounter{enumicounter}{value{enumi}} %save the enumeration counter

            end{enumerate}

            section{another section}

            More Text Text Text Text Text Text Text Text Text Text Text Text Text Text Text Text Text Text Text Text

            subsection{a subsection}

            More Text Text Text Text Text Text Text Text Text Text Text Text Text Text Text Text Text Text Text Text

        end{emailresume}

        More

        begin{emailresume}

            subsection{another subsection}

            More Text Text Text Text Text Text Text Text Text Text Text Text Text Text Text Text Text Text Text Text

        end{emailresume}

        More

        begin{emailresume}

            Bye,



            Sheß

        end{emailresume}

        Bye,



        Einstein

    end{emailresume}

    Bye

end{document}

All I did here is to slightly modify Gonzalo Medina's nice answer. One can of course tune it a bit more. (I also understand that there is nothing squiggly here, I was too lazy to rename the macros.)

documentclass{article}

usepackage{refcount}

usepackage{tikz}

usetikzlibrary{calc,tikzmark}

usepackage{lipsum}



newcounter{tmp}

% newcommandtikzmark[1]{%

%   tikz[overlay,remember picture] node (#1) {};}



newcommandStartsquiggly{%

  stepcounter{tmp}%

  tikzmarknode{a}{strut}label{athetmp}%

  ifnumgetpagerefnumber{athetmp}=getpagerefnumber{bthetmp} else

  begin{tikzpicture}[overlay, remember picture]

    draw [ultra thick,gray]

      let p1 = (a.south), p2 = (b), p3 = (current page.center) in

      ( $ (x3,y1) + (-.55textwidth,0) $ ) --  ( $ (x3,y3) + (-0.55textwidth,-0.5textheight) $ );

  end{tikzpicture}%

  fi%

}



newcommandEndsquiggly{%

tikzmarknode{b}{strut}label{bthetmp}

  ifnumgetpagerefnumber{athetmp}=getpagerefnumber{bthetmp}

  begin{tikzpicture}[overlay, remember picture]

    draw [ultra thick,gray]

      let p1 = (a.south), p2 = (b), p3 = (current page.center) in

      ( $ (x3,y1) + (-.55textwidth,1em) $ ) --  ( $ (x3,y2) + (-.55textwidth,1em) $ );

  end{tikzpicture}%

  else

  begin{tikzpicture}[overlay, remember picture]

    draw [ultra thick,gray]

      let p1 = (a.south), p2 = (b), p3 = (current page.center) in

      ( $ (x3,y3) + (-.55textwidth,.5textheight) $ ) -- ( $ (x3,y2) + (-.55textwidth,1em) $ );

  end{tikzpicture}%

  fi

}



newcommandSqu[1]{Startsquiggly#1Endsquiggly}

AtBeginDocument{Startsquiggly}

AtEndDocument{parEndsquiggly}

newcommand{response}[1]{parEndsquiggly#1parStartsquiggly}

begin{document}

Some text, with pictures, lists, sections

begin{enumerate}

item Some text, with pictures, lists, sections

response{answer1}

item Some text, with pictures, lists, sections

response{answer2}

end{enumerate}

Some text, with pictures, lists, sections

response{this is my answer}

Some text, with pictures, lists, sections

section{section}

subsection{subsection1}

Some text, with pictures, lists, sections

subsection{subsection2}

Some text, with pictures, lists, sections

subsection{subsection3}

Some text, with pictures, lists, sections

response{I also have an answer here}

More text

end{document}

A solution I came up with, but I'm still fairly unhappy with the amount of things that are hard-coded. E.g.

• it requires that I change all begin{enumerate}[some arguments] to begin{enumerate}{some arguments}
  


• works only for up to a fixed number of nested enumerates and


• probably fails if the original document uses an itemize or something else.


• it cannot be nested

So, eventhough I'm posting this as an aswer to my own post, I do not consider this complete and would be happy for anyone who adapts it to be more general

documentclass{article}



newcounter{breakdepth}

usepackage{enumitem}

usepackage{letltxmacro}



%redefine enumerates so that they are automatically resumable

LetLtxMacroooenumerateenumerate

LetLtxMacroendooenumerateendenumerate

makeatletter

    renewenvironment{enumerate}[2][0]{%

        ifx0#1%i.e. this is not a resume, but a new list, so start naming it.

            ooenumerate[series=levelthe@enumdepth,#2]%

        else

            ooenumerate[#2]%

        fi

    }{

         endooenumerate%

    }

%define the command that breaks the report environment, closes all enumerates, but resumes them afterwards

newcommand{response}[1]{%

setcounter{breakdepth}{the@enumdepth}%

ifnumvalue{breakdepth}>3  end{enumerate} fi%

ifnumvalue{breakdepth}>2  end{enumerate} fi%

ifnumvalue{breakdepth}>1  end{enumerate} fi%

ifnumvalue{breakdepth}>0  end{enumerate} fi%

end{report}%

#1%

begin{report}%

ifnumvalue{breakdepth}>0  begin{enumerate}{resume*=levelthe@enumdepth}itemfi%

ifnumvalue{breakdepth}>1  begin{enumerate}{resume*=levelthe@enumdepth}itemfi%

ifnumvalue{breakdepth}>2  begin{enumerate}{resume*=levelthe@enumdepth}itemfi%

ifnumvalue{breakdepth}>3  begin{enumerate}{resume*=levelthe@enumdepth}itemfi%

}

makeatother

%define the environment that has a slight indentation and a vertical line for the original text

usepackage{mdframed}

newenvironment{report}{begin{mdframed}[linewidth=1pt,topline=false,rightline=false,bottomline=false,linecolor=black,innerleftmargin =0cm, leftmargin=2pt,innerrightmargin=1pt]}{end{mdframed}}



begin{document}

    begin{report}

    section{first section}

    begin{enumerate}{label=roman*.}

    item ione 

    begin{enumerate}{}

    item aone

    %%%%%%%%%

    response{test} 

    %%%%%%%%%

    item atwo

    end{enumerate}

    item itwo

    response{test} 

    end{enumerate}

    section{a section}

    Some text that is not inside a list

    response{test} 

    more text

    end{report}

end{document}