I had to mess with the settings of the book class to match people's will. Removing the "Chapter X \\ Xtitle" part and replacing it with "X. Xtitle" for instance. In verdana 14 (so I compile with XeLaTeX, also because the body text is written in Perpetua, 13pt).
Anyway, I whittled my code down to the following MWE. How do I get rid of "0. Chapter title" in \frontmatter book chapter titles? But I do want to keep "Chapter title".
\documentclass{book}
\usepackage{lipsum}
\usepackage{fontspec} % compile w/XeLaTeX
\setmainfont{Perpetua}
\newfontfamily\chapterfont{Verdana}
\makeatletter % https://tex.stackexchange.com/questions/18604/chapter-formatting
\def@makechapterhead#1{%
{\parindent \z@ \raggedright \chapterfont\fontsize{14pt}{0pt}\bfseries
\ifnum \c@secnumdepth >\m@ne
\thechapter.\ % <-- Chapter # (without "Chapter")
\fi
\interlinepenalty@M
#1\par\nobreak% <------------------ Chapter title
\vskip 12pt% <------------------ Space between chapter title and first paragraph
}}
\makeatother
\begin{document}
\frontmatter
\chapter{Preface}
\lipsum
\chapter{Abstract}
\lipsum
\tableofcontents
\mainmatter
\chapter{A chapter}
\lipsum
\chapter{Another chapter}
\lipsum
\end{document}
Any thoughts?
Edited to include fontspec and some settings in the package to remove the most egregious errors in the MWE.There are a few commands that are terminated with a space which is code copied from another answer.
\chapter*you should also redefine\@makeschapterhead(notice the 's' for starred) as you did for\@makechapterheadjust omitting the\thechapter. – Jhor Apr 07 '23 at 10:25