Sectioning command that automatically creates label

Question

I'm trying to define a custom section command that will also define a corresponding label after a bit of preparsing. Specifically, I want the command to define a section with the given name, and then define a label with the name lower-cased and having spaces replaced with dashes.

So far I've come up with the following:

\NewDocumentCommand\startSection{m}
{
  \section{#1}\label{\lowercase{\StrSubstitute{#1}{ }{-}}}
}

Which uses the xstring and xparse packages, but this yields an error:

! Argument of \@sect has an extra }.

After a bit of playing around I would get:

! Missing \endcsname inserted

around the \lowercase command.

I seem to be missing some essential knowledge about how labels work, so does anyone have a good suggestion?

Answer 1

\usepackage{xstring}
\newcommand{\startSection}[1]{%
  \lowercase{\def\templabel{#1}}%
  \StrSubstitute{\templabel}{ }{-}[\templabel]
  \section{#1}\label{\templabel}}

The \StrSubstitute and \lowercase commands are not expandable, so your \label doesn't find anything good for it. You have to \lowercase first, then to \StrSubstitute and finally feed the string to \label.

However, it's just an exercise: this command will probably break if accented letters or commands are in the section title.