Extend chapter heading numbers into margin

Question

In my earlier question, I got a very helpful response on extending section headings in a KomaScript article document into the margins: Extending section heading underline into margin

The MWE answer was:

\PassOptionsToPackage{svgnames,table,dvipsnames}{xcolor}
\documentclass[a4paper,10pt,oneside,DIV=9]{scrartcl}
% Packages
\usepackage{scrlayer-scrpage}
\usepackage{xcolor} % showframe loads this
\usepackage[normalem]{ulem}
\usepackage{hyperref}
% demo only
\usepackage{lipsum}
\usepackage{mwe}
% theme colours
\definecolor{MyThemeColour}{cmyk}{0.10,0.10,1.00,0} % personal yellow
\newlength{\mysecnumhang}
\setlength{\mysecnumhang}{30pt}
% KOMA and general setup
\renewcommand{\sectionformat}{%
  \makebox[\mysecnumhang][l]{\thesection\autodot\enskip}%
}
\renewcommand{\subsectionformat}{%
  \makebox[\mysecnumhang][l]{\thesubsection\autodot\enskip}%
}
\renewcommand*{\subsubsectionformat}{%
  \makebox[\mysecnumhang][l]{\thesubsubsection\autodot\enskip}%
}
\newbox\tmpseclinenobox
\renewcommand{\sectionlinesformat}[4]{%
  \sbox\tmpseclinenobox{#3}%
  \ifdim\wd\tmpseclinenobox>0pt\hspace{-\mysecnumhang}\fi
  \expandafter\headuline{#3#4}%
}
\newcommand\headuline{%
    \bgroup\markoverwith{\textcolor{MyThemeColour}{\rule[-0.75ex]{1pt}{1pt}}}\ULon% 2pt 2pt
    }
% recalc the text block after all the font loading
\KOMAoptions{DIV=last}
\begin{document}
\section*{Lipsum}
Some text.
\section{Lipsum}
\blinddocument
\end{document}

If I change the class to scrbook and add some `\chapter{}\s to it, I can't seem to replicate the effect with the chapter headings.

Would anyone feel able to update the MWE to deal with chapters?

Answer 1

Redefine \chapterformat in the same way:

\renewcommand*{\chapterformat}{%
  \makebox[\mysecnumhang][l]{\thechapter\autodot\enskip}%
}

and redefine \chapterlinesformat:

\renewcommand{\chapterlinesformat}[3]{%
  \sbox\tmpseclinenobox{#2}%
  \ifdim\wd\tmpseclinenobox>0pt\hspace{-\mysecnumhang}\fi
  \expandafter\headuline{#2#3}%
}

or

\renewcommand{\chapterlinesformat}[3]{%
  \Ifstr{#2}{}{}{\hspace{-\mysecnumhang}}%
  \expandafter\headuline{#2#3}%
}

Example:

\PassOptionsToPackage{svgnames,table,dvipsnames}{xcolor}
\documentclass[a4paper,10pt,oneside,DIV=9]{scrbook}
% demo only
\usepackage{mwe}
% Packages
\usepackage{scrlayer-scrpage}
\usepackage{xcolor} % showframe loads this
\usepackage[normalem]{ulem}
\usepackage{hyperref}
% theme colours
\definecolor{MyThemeColour}{cmyk}{0.10,0.10,1.00,0} % personal yellow
\newlength{\mysecnumhang}
\setlength{\mysecnumhang}{30pt}
% KOMA and general setup
\renewcommand{\chapterformat}{%
  \makebox[\mysecnumhang][l]{\thechapter\autodot\enskip}%
}
\renewcommand{\sectionformat}{%
  \makebox[\mysecnumhang][l]{\thesection\autodot\enskip}%
}
\renewcommand{\subsectionformat}{%
  \makebox[\mysecnumhang][l]{\thesubsection\autodot\enskip}%
}
\renewcommand{\subsubsectionformat}{%
  \makebox[\mysecnumhang][l]{\thesubsubsection\autodot\enskip}%
}
\renewcommand{\chapterlinesformat}[3]{%
  \Ifstr{#2}{}{}{\hspace{-\mysecnumhang}}%
  \expandafter\headuline{#2#3}%
}
\renewcommand{\sectionlinesformat}[4]{%
  \Ifstr{#3}{}{}{\hspace{-\mysecnumhang}}%
  \expandafter\headuline{#3#4}%
}
\newcommand\headuline{%
  \bgroup\markoverwith{\textcolor{MyThemeColour}{\rule[-0.75ex]{1pt}{1pt}}}\ULon% 2pt 2pt
}
% recalc the text block after all the font loading
\KOMAoptions{DIV=last}
\begin{document}
\addchap{Foo}
\addsec*{Lipsum}
Some text.
\section{Lipsum}
\blinddocument
\end{document}

Additional remark: The solution is limited to one line headings because of the underline.

---

Regarding a comment below:

If you visualize the bounding box of the letters in the headings (using eg. https://tex.stackexchange.com/a/57860), the alignment of the heading texts will be visible:

Code for the picture:

\PassOptionsToPackage{svgnames,table,dvipsnames}{xcolor}
\documentclass[a4paper,10pt,oneside,DIV=9]{scrbook}
% demo only
\usepackage{mwe}
% Packages
\usepackage{scrlayer-scrpage}
\usepackage{xcolor} % showframe loads this
\usepackage[normalem]{ulem}
%\usepackage{hyperref}
% theme colours
\definecolor{MyThemeColour}{cmyk}{0.10,0.10,1.00,0} % personal yellow
\newlength{\mysecnumhang}
\setlength{\mysecnumhang}{30pt}
% KOMA and general setup
\renewcommand{\chapterformat}{%
  \makebox[\mysecnumhang][l]{\thechapter\autodot\enskip}%
}
\renewcommand{\sectionformat}{%
  \makebox[\mysecnumhang][l]{\thesection\autodot\enskip}%
}
\renewcommand{\subsectionformat}{%
  \makebox[\mysecnumhang][l]{\thesubsection\autodot\enskip}%
}
\renewcommand{\subsubsectionformat}{%
  \makebox[\mysecnumhang][l]{\thesubsubsection\autodot\enskip}%
}
\renewcommand{\chapterlinesformat}[3]{%
  \Ifstr{#2}{}{}{\hspace{-\mysecnumhang}}%
  \expandafter\headuline{#2#3}%
}
\renewcommand{\sectionlinesformat}[4]{%
  \Ifstr{#3}{}{}{\hspace{-\mysecnumhang}}%
  \expandafter\headuline{#3#4}%
}
\newcommand\headuline{%
  \bgroup\markoverwith{\textcolor{MyThemeColour}{\rule[-0.75ex]{1pt}{1pt}}}\ULon% 2pt 2pt
}
% recalc the text block after all the font loading
\KOMAoptions{DIV=last}
% show bounding box for each letter (https://tex.stackexchange.com/a/57860)
\makeatletter
\def\showboxes#1{%
  \begingroup\color{red}\fboxrule=.1pt \fboxsep=-\fboxrule
  @showboxes#1@showboxes@empty
  \endgroup}
\def@showboxes#1#2{%
  \ifx#2@showboxes
    \fbox{\color{gray}#1}\expandafter@gobble
  \else
    \setbox0=\hbox{#1\kern0pt#2}\setbox2=\hbox{#1#2}%
    \dimen0=\wd0 \advance\dimen0 -\wd2 % \dimen0 contains the kern between the two chars
    \fbox{\color{gray}#1}\kern-\dimen0
    \expandafter@showboxes
  \fi#2}
\begin{document}
\chapter{\showboxes{Lipsum}}
\section{\showboxes{Lipsum}}
\end{document}