doc update

1 files changed, 4 insertions, 0 deletions

diff --git a/docs/env_variables.txt b/docs/env_variables.txt
index cea3597b..4a39cc9a 100644
--- a/docs/env_variables.txt
+++ b/docs/env_variables.txt
@@ -201,6 +201,10 @@ checks or alter some of the more exotic semantics of the tool:
     mutated files - say, to fix up checksums. See experimental/post_library/
     for more.
 
+  - Setting AFL_CUSTOM_MUTATOR_LIBRARY to a shared library with
+    afl_custom_mutator() export will run all mutations solely to this function.
+    see docs/custom_mutator.txt
+
   - For AFL_PYTHON_MODULE and AFL_PYTHON_ONLY - they require to be compiled
     with -DUSE_PYTHON. Please see docs/python_mutators.txt
     This feature allows to configure custom mutators which can be very helpful