diff --git a/docs/manifest-format.txt b/docs/manifest-format.txt
index 0e6cbe3..56bdf14 100644
--- a/docs/manifest-format.txt
+++ b/docs/manifest-format.txt
@@ -86,6 +86,7 @@
     <!ATTLIST extend-project name CDATA #REQUIRED>
     <!ATTLIST extend-project path CDATA #IMPLIED>
     <!ATTLIST extend-project groups CDATA #IMPLIED>
+    <!ATTLIST extend-project revision CDATA #IMPLIED>
 
     <!ELEMENT remove-project EMPTY>
     <!ATTLIST remove-project name  CDATA #REQUIRED>
@@ -300,6 +301,9 @@
 Attribute `groups`: List of additional groups to which this project
 belongs.  Same syntax as the corresponding element of `project`.
 
+Attribute `revision`: If specified, overrides the revision of the original
+project.  Same syntax as the corresponding element of `project`.
+
 Element annotation
 ------------------