Morten Høgholm wrote:

[snip]
> From l3messages:
> 
> % \begin{macro}{\text_put_sp:}
> % \begin{macro}{\text_put_four_sp:}
> %    We need these functions for certain error and warning messages
> %    right away. They put one and four spaces into the message stream.
> %    \begin{macrocode}
> \def_new:Npn \text_put_sp: {~}
> \def_new:Npn \text_put_four_sp: {\text_put_sp: \text_put_sp:
>                                  \text_put_sp: \text_put_sp: }
> %    \end{macrocode}
> % \end{macro}
> % \end{macro}
> %

As you may have guessed, I'm using source quite heavily for finding
things I suspect may exist.  \text_put_sp: is not in the "documentation"
part of source3, so doesn't show up by default.  Looking at l3messages,
it seems there is quite a bit that doesn't make it to the "use" part.  I
shall read the implementation properly on this.
-- 
Joseph Wright