On 20/08/2012 21:42, Joel C. Salomon wrote:
> The intent of \tn seems to be providing a \cs-like macro that puts its
> argument in a different index section for TeX/LaTeX2e commands (though
> this is not implemented, or at least not working, at the moment).
> 
> How relevant is this, outside the l3 project itself?  Is there any
> real reason for me to make this distinction in xpeek?
> 
> —Joel

The idea is exactly as you say. Long-term, we may want to enhance this
difference. Thus I would recommend using \tn for LaTeX2e and TeX
commands, and \cs for LaTeX3-related material.
-- 
Joseph Wright