[NTG-context] Understanding registers command

[Taco Hoekwater]

This looked suspiciously familiar. And indeed, my bib module has the same
problem:

  % Hans, Wat is er mis met [pub][pubs]???
  % Werkt absoluut niet!
  
  \definieerlijst[pubs][pubs]

Greetings, Taco

> \definieerregister
>    [\v!index]
>    [\v!index]
>