--- a/doc/hgrc.5.txt
+++ b/doc/hgrc.5.txt
@@ -327,6 +327,11 @@ hooks::
Also, hooks like "commit" will be called in all contexts that
generate a commit (eg. tag) and not just the commit command.
+ Note2: Environment variables with empty values may not be passed to
+ hooks on platforms like Windows. For instance, $HG_PARENT2 will
+ not be available under Windows for non-merge changesets while being
+ set to an empty value under Unix-like systems.
+
The syntax for Python hooks is as follows:
hookname = python:modulename.submodule.callable