Trouble understanding \titlelabel, \thesection, \thesubsection, \thetitle

Question

I am reading the document for titlesec package. There is a command called \titlelabel{<lable-format>} and the document says:

"Changes the label format in sections, subsections, etc. A \thetitle command is provided which is respectively \thesection, \thesubsection, etc. The default value in standard classes is..."

I am wondering about what \thetitle, \thesection, \thesubsection do.

Answer 1

The commands \thesection, \thesubsection, etc. are commands of any standard document class that show the actual formatted numeration for \section, \subsection, etc. as. I mean that could print some like "3.3" or "III.c" depending of how they are defined.

For example, in the article document class by default \thesection is defined as \@arabic\c@section than mean \arabic{section} (here section without \ is the name of the counter) whereas for \thesubsection is \thesection .\@arabic \c@subsection (i.e, \arabic{section}.\arabic{subsection}), etc.

The \thetitle is a wildcard to the above comnands of the titlesec package, so after a \section{} will be \csname thesection\endcsname and after a \subsection{} will be \csname thesubsection\endcsname, etc. You can see in the next MWE how \thetitle change to be equal to \thesection or the \thesubsection depending on its position into the text:

\documentclass{article}
\usepackage{titlesec}
\titlelabel{\thetitle\quad---\quad} % "original" format beside \thetitle
\begin{document}
\section{First section}
This is the section \thesection \\
This is the subsection \thesubsection \\
This is the title \thetitle
\section{Second  section}
This is the section \thesection \\
This is the subsection \thesubsection \\
This is the title \thetitle
\subsection{First subsection}
This is the section \thesection \\
This is the subsection \thesubsection \\
This is the title \thetitle
\end{document}