doc/cmd/Tracing | 3 ++-

diff --git a/doc/cmd/Tracing b/doc/cmd/Tracing
index d95523504a8b4a395382c39dc7d5d40134f1804d06d6da11a57b060ee0367faa..d034e26cc753e55e5a0f65fe6ba1a43c0fa5f8197dea98c1b25b5736ddc3bd4e 100644
--- a/doc/cmd/Tracing
+++ b/doc/cmd/Tracing
@@ -1,3 +1,4 @@
+A [Env] REDO_TRACE
 -x option can be used to enable tracing (set -x) of the currently run
 shell script .do file. -xx option enables tracing for all invoked .do
-files further.
+files further, which just sets $REDO_TRACE=1 environment variable.