Title format defined with titlesec: How to use it outside \chapter?

Question

I am using titlesec to define the format of my chapter titles, for instance:

\titleformat{\chapter}[hang]{\Large\bfseries}{}{0em}{\LARGE\bfseries}

I would like to be able to specify the same format (i.e., extract the \LARGE\bfseries bit) for a portion of normal text.

Motivation: I am typesetting an anthology where one of the authors occasionally starts a new chapter alongside a figure, in a table, inbetween paragraphs, and so on. So while most of my chapters start on a new page and I don't want to change the default, I need to "fake" a new chapter in several places. My idea is to set it with font defined by \titleformat, increment counters if necessary (the book does not have numbered chapters so probably not) and add to contents with \addcontentsline.

Answer 1

Here's a simple solution. It defines a \nobreakchapter command that behaves just like \chapter but suppresses the pagebreak. To do this I've created a boolean \ifnbchap which gets set to true by the \nobreakchapter. Then this boolean is used inside a patched \chapter command to skip the pagebreak code. Since your question is quite sketchy on more details I haven't done anything else to format this type of chapter. I reset the \nbchap conditional to false using the titlesec end code, so that you can use that conditional to also affect any formatting requirements (e.g. vertical spacing) you might need for the \nobreakchapter command.

In response to the comment, I've also eliminated the \thispagestyle{plain} command from the \nobreakchapter chapters.

\documentclass{book}
\usepackage{titlesec}
\titleformat{\chapter}[hang]{\Large\bfseries}{}{0em}{\LARGE\bfseries}[\global\nbchapfalse]
\usepackage{xpatch}
\usepackage{kantlipsum} % for dummy text
\newif\ifnbchap
\xpretocmd{\chapter}{\ifnbchap\else}{}{}
\xpatchcmd{\chapter}{\clearpage\fi}{\clearpage\fi\fi}{}{}
\xpatchcmd{\chapter}{\thispagestyle{plain}}{\ifnbchap\else\thispagestyle{plain}\fi}{}{}
\newcommand{\nobreakchapter}{\nbchaptrue\chapter}
\begin{document}
\frontmatter
\tableofcontents
\mainmatter
\chapter{This is a regular chapter}
\kant
\chapter{This is another regular chapter}
\kant[1]
\nobreakchapter{This is a no break chapter}
\kant[2]
\nobreakchapter{This is another no break chapter}
\kant
\chapter{Another regular chapter}
\kant
\nobreakchapter{A nobreak chapter} 
\kant[1]
\chapter{Another regular chapter}
\kant
\end{document}