Why does LaTeX (contrarily to TeX) not allow catcode changes in footnotes?

Question

In Plain TeX the following compiles with no error

Hello\footnote*{\tt\catcode92=12 \world}!
\bye

The analog in LaTeX

\documentclass{article}
\begin{document}
Hello\footnote{\ttfamily\catcode92=12 \world}!
\end{document}

fails with error message

 ERROR: Undefined control sequence.

 --- TeX said --- <argument> ...ces \ttfamily \catcode 92=12 \world 
                                                   \@finalstrut \strutbox  l.4 Hello\footnote{\ttfamily\catcode92=12 \world}
                                                  !

which just says that \world was still seen as an undefined control sequence. So it is as if the (mandatory) argument to \footnote was treated as is usual with macro arguments and the consequence is that one can not use \verb in the LaTeX footnotes.

What are the rationale or implementation constraints which led to this impoverished (in that respect) \footnote concept in LaTeX?

Answer 1

LaTeX has always done this. Certainly at LaTeX2e it was a concious decision not to change it. The documented behaviour is that \verb does not work in the argument of another command. If you make it work in \footnote you have to explain why it doesn't work in \marginpar or in \footnote that is inside \textrm{...} or any other place it would fail. Basically LaTeX does not support changing catcodes mid-document. There are almost always better more robust techniques that could be used, for example \footnote{\ttfamily\string\world} works in LaTeX even if that is already in the argument of another macro.

Answer 2

FWIW, this snippet works in ConTeXt.

\starttext
Hello\footnote{\tt\catcode92=12 \world}!
\stoptext

but, as pointed out by David, it fails for \inmargin (which is the ConTeXt equivalent of \marginpar). This is not surprising; all catcode changes fail with macros that parse their argument. Having said that, the standard way in ConTeXt to take care of catcode changes is to use buffers.

\starttext
\startbuffer[catcode]
\catcode92=12 \world
\stopbuffer
Hello\inmargin{\tt\getbuffer[catcode]}!
\stoptext

which works correctly in both MkII and MkIV. In LaTeX, the filecontents environment is the closest to buffers. (See LaTeX equivalent of ConTeXt buffers).