Hanging indentation with linguex (Why does this work?)

Question

I wanted to create linguex examples where the free translation line has a hanging indent of 21.3 big points. I found that use of the hanging package, which is simple enough, does not work (second example in code). Reading the relevant section of the TeXbook (after three days) yielded a less simple solution which does work (first example in code). Why does use of the hanging package fail?

\tracingmacros=1
\documentclass{article}
\usepackage{hanging}
\usepackage{linguex}
\usepackage{lipsum}

\begin{document}

\ex .
\gll    Mundus vult decipi      \\
        world want deceive      \\
\glt    \dimen0=\the\textwidth
        \dimen1=\the\textwidth
        \dimen2=21.3bp
        \advance\dimen0 by -\the\labelwidth
        \advance\dimen1 by -\the\labelwidth
        \advance\dimen1 by -\dimen2
        \advance\dimen2 by \the\labelwidth
        \parshape=2 \the\labelwidth \dimen0 \dimen2 \dimen1
        \lipsum[2]



\ex .
\gll    Mundus vult decipi      \\
        world want deceive      \\
\glt    \hangpara{21.3bp}{2}\lipsum[2]

\end{document}

Output of the above code is as follows:

Answer 1

As Alan Munn says in his comment, linguex basically uses list environments; inside a list environment at every paragraph start an instruction \parshape1 is executed, which wins over setting \hangindent. So any setting to \hangindent is ignored. You can use a list yourself: the setting is not difficult at all:

\documentclass{article}
\usepackage{linguex}
\usepackage{lipsum}

\begin{document}

\ex .
\gll  Mundus vult decipi \\
      world want deceive \\
\glt  \begin{list}{}{%
        \leftmargin=21.3pt
        \itemindent=-\leftmargin}
      \item[]\lipsum*[2]
      \end{list}

\end{document}

You probably want to define your own environment for this:

\newcommand{myindentedpar}[1][21.3pt]
 {\begin{list}{}{\leftmargin=#1 \itemindent=-\leftmargin}\item[]}
 {\end{list}}

so the above can be specified as

\glt  \begin{myindentedpar}
      \lipsum*[2]
      \end{myindentedpar}

A different amount of indentation can be specified in the optional argument

\begin{myindentedpar}[30pt]
\lipsum*[2]
\end{myindentedpar}

Here's the result with 21.3pt: