[texhax] Constructing a very thin space

[Philip Taylor]

Axel E. Retif wrote:

> You can make your own thin spaces putting something like this in your
> preamble:
> 
> \def\mythinspace{\kern 0.1em }
> \def\myverythinspace{\kern 0.05em }
> 
> You can make negative thin spaces as well. The space between ...em and
> the closing bracket is *very* important.

Forgive my naïvety, but /why/ is the space important ?
The operator is a kern, not a skip, so neither plus
nor minus modifiers may follow; what (if the space
were omitted) could accidentally follow the brace
to foul things up ?

** Phil.