tcl8.4.3 file doc/tclvars.n
refers to tcl_traceExec and tcl_traceCompile,
just as it always has. However, with the tcl8.4.3
release, these variables are only predefined and bound
if the tcl code was compiled with TCL_COMPILE_DEBUG,
which is not the default with out-of-the-box builds.
The documentation needs to be updated to say when these
variables are predefined and bound.