# [NTG-context] Unexpected emergency stop

Wolfgang Schuster schuster.wolfgang at gmail.com
Sat Feb 10 13:45:29 CET 2018

> Tim Steenvoorden <mailto:tim.steenvoorden at gmail.com>
> 10. Februar 2018 um 12:44
> Thanks Otared! Works like a charm!
>
> Out of curiosity, could you explain the mechanics behind this? I know
> it is a commonly used trick in TeX macro definitions, but I don’t know
> how it changes TeX’s understanding of the tokes it parses.

When you create a new commands like this

\def\mycommand[#1]{...}

the brackets are delimiters for the argument of the command, i.e. when
TeX sees
\mycommand it looks for [ and grabs everything intill ] as as argument.
When you
out now a space (or start a new line) after ] in your definition of the
command, e.g.

\def\mycommand[#1] {...}

TeX looks now for “] ” (right bracket followed by a space) as delimiter for