[Tex/LaTex] find help files or documentation for commands like \@startsection for LaTeX

Question

I can't find official documentation for the \@startsection command.
I already looked in:

1. LaTeX Wikibook
2. LaTeX: Structured document for TEX, 2008
3. beginLatex — a book that comes with ProTeX
4. in the files that comes with MikTeX in the folder doc

and Google.
I found a lot of sites that show examples and discussions about it but I'd like to find the official help or document.

Answer 1

The actual command, including its formal definition posted by @JoshLee is contained in the LaTeX 2e source, section 61.2 Sectioning (p 283). It forms part of ltsect.dtx, the bundle containing all sectioning commands for LaTeX. It even includes a pseudo-code interpretation of the actual macro. Here is an extract:

The \@startsection{<name>}{<level>}{<indent>}{<beforeskip>}{<afterskip>}{<style>}*[<altheading>]{<heading>} command is the mother of all the user level sectioning commands. The part after the *, including the * is optional.

• name: e.g., subsection
• level: a number, denoting depth of section - e.g., chapter = 0, section = 1, etc.
• indent: Indentation of heading from left margin
• beforeskip: Absolute value = skip to leave above the heading. If negative, then paragraph indent of text following heading is suppressed.
• afterskip: If positive, then skip to leave below heading, else negative of skip to leave to right of run-in heading.
• style: Commands to set style. Since June 1996 release the last command in this argument may be a command such as \MakeUppercase or \fbox that takes an argument. The section heading will be supplied as the argument to this command. So setting #6 to, say, \bfseries\MakeUppercase would produce bold, uppercase headings.

If * is missing, then increment the counter. If it is present, then there should be no [<altheading>] argument. The command uses the counter secnumdepth. It contains a pointer to the highest section level that is to be numbered.