diff --git a/Help/variable/PROJECT-NAME_IS_TOP_LEVEL.rst b/Help/variable/PROJECT-NAME_IS_TOP_LEVEL.rst
index 953e978..6718ecf 100644
--- a/Help/variable/PROJECT-NAME_IS_TOP_LEVEL.rst
+++ b/Help/variable/PROJECT-NAME_IS_TOP_LEVEL.rst
@@ -9,3 +9,13 @@
 To obtain the value from the most recent call to :command:`project` in
 the current directory scope or above, see the
 :variable:`PROJECT_IS_TOP_LEVEL` variable.
+
+The variable value will be true in:
+
+* the top-level directory of the project
+* the top-level directory of an external project added by :module:`ExternalProject`
+
+The variable value will be false in:
+
+* a directory added by :command:`add_subdirectory`
+* a directory added by :module:`FetchContent`
diff --git a/Help/variable/PROJECT_IS_TOP_LEVEL.rst b/Help/variable/PROJECT_IS_TOP_LEVEL.rst
index e5eb6c1..ad61fec 100644
--- a/Help/variable/PROJECT_IS_TOP_LEVEL.rst
+++ b/Help/variable/PROJECT_IS_TOP_LEVEL.rst
@@ -19,3 +19,13 @@
   if(PROJECT_IS_TOP_LEVEL)
     include(CTest)
   endif()
+
+The variable value will be true in:
+
+* the top-level directory of the project
+* the top-level directory of an external project added by :module:`ExternalProject`
+
+The variable value will be false in:
+
+* a directory added by :command:`add_subdirectory`
+* a directory added by :module:`FetchContent`