Frank Mittelbach wrote:

> Will Robertson writes:

>  > This is weird:

>  > 

>  >    \err_warn:nn{\temp~stuff~stuff}{}

>  > 

>  > Only the second tilde causes a space.

> 

> why would that be weird?

> 

> in plain TeX

> 

>   \errwarn{\temp stuff stuff} 

> 

> and only

> 

>   \errwarn{\temp\space stuff stuff}

> 

> in expl3 ~ is a space token and not an active char expanding to \space.



It took me a little while to realise this, but of course you are right.

 So that was not what confused me.



> It is a bitof a pity that space tokens are so deep down within the TeX engine

> behavior and that sometimes they get gobbled if explicit.

> 

> Interesting question if it would be possible to do ~ -> \space instead but my

> guess is that this would break a lot of the current code



I was rather expecting \c_space_token to save the day, but it didn't.

Hence my confusion: \space isn't a LaTeX3 name.

-- 

Joseph Wright