Mittelbach, Frank wrote:

> philosophically tpls (token list pointers) have been invented precisely to be used to store data and not use "function definitions" for this (technically it uses \def:Npn of course, but it can for example do additional checks).

Good idea.  Perhaps the docs could mention this, to explain to existing
(La)TeX coders that there is meant to clean separation between macros
and storage (even though they both do the same thing "underneath).

A quick overview of the different storage types and their intended use
might be handy.  You have to read quite a bit to even begin to get it
(and so far I am obviously not quite there!).
-- 
Joseph Wright