Help: Clarify and update SYSTEM-related docs

1 files changed, 11 insertions, 6 deletions

diff --git a/Modules/FetchContent.cmake b/Modules/FetchContent.cmake
index 25b0683d36..047603cbdc 100644
--- a/Modules/FetchContent.cmake
+++ b/Modules/FetchContent.cmake
@@ -233,12 +233,12 @@ Commands
   .. versionadded:: 3.25
 
     ``SYSTEM``
-      If the ``SYSTEM`` argument is provided, targets created by
-      the dependency will have their :prop_tgt:`SYSTEM` property
-      set to true when populated by :command:`FetchContent_MakeAvailable`.
-      The entries in their  :prop_tgt:`INTERFACE_INCLUDE_DIRECTORIES`
-      will be treated as ``SYSTEM`` include directories when
-      compiling consumers.
+      If the ``SYSTEM`` argument is provided, the :prop_dir:`SYSTEM` directory
+      property of a subdirectory added by
+      :command:`FetchContent_MakeAvailable` will be set to true.  This will
+      affect non-imported targets created as part of that command.
+      See the :prop_tgt:`SYSTEM` target property documentation for a more
+      detailed discussion of the effects.
 
 .. command:: FetchContent_MakeAvailable
 
@@ -353,6 +353,11 @@ Commands
       adding a project that contains a ``CMakeLists.txt`` file in its top
       directory.
 
+    .. versionadded:: 3.25
+      If the ``SYSTEM`` keyword was included in the call to
+      :command:`FetchContent_Declare`, the ``SYSTEM`` keyword will be
+      added to the :command:`add_subdirectory` command as well.
+
   Projects should aim to declare the details of all dependencies they might
   use before they call ``FetchContent_MakeAvailable()`` for any of them.
   This ensures that if any of the dependencies are also sub-dependencies of