restricted system commands enabled.
(./tracing.tex
{\def}
{blank space }
{\message}
\a #1#2->[#1|#2]
#1<-x
#2<-yz
[x|yz]
{blank space }
{\count}
{undefined}
! Undefined control sequence.
l.5 \count1=\numexpr
1+2\relax
{the character +}
{horizontal mode: the character +}
{the character 2}
{\relax}
{\tracingmacros}
{\tracingcommands}
[0.1])
(see the transcript file for additional information)
Output written on tracing.dvi (1 page, 132 bytes).
Transcript written on tracing.log.