manual/files/blend/compatibility.rst

@@ -0,0 +1,58 @@
+
+*************
+Compatibility
+*************
+
+Blender can open blend-files saved with both older versions of the software (backward compatibility),
+and newer ones (forward compatibility). This comes with some limitations though.
+
+.. tip::
+
+   When having issues with opening much older (or newer) blend-files, it can help to use a few
+   intermediary Blender releases to perform conversions by smaller steps.
+
+.. note::
+
+   Here is a `more exhaustive documentation <https://wiki.blender.org/wiki/Process/Compatibility_Handling>`__
+   about compatibility handling, in the developpers documentation.
+
+
+Backward Compatibility
+======================
+
+Opening older files and converting them for the current version of Blender is usually straight-forward.
+It is expected to give very good and usable results.
+
+There can be major feature changes, for which the backward compatibility will only be ensured for
+a limited amount of time. For example the changes to the animation system that happened during the
+Blender 2.5x project. This will never be less than a full major release cycle (i.e. two years at least).
+
+
+Forward Compatibility
+=====================
+
+Loss of Data
+------------
+
+Forward compatibility is inherently harder to ensure, and loss of feature should always be expected
+when opening a blend-file saved with a more recent version of Blender.
+
+A warning is shown in the UI when editing a more recent blend-file.
+Trying to overwrite it (with a simple 'Save' operation) will also show a confirmation popup,
+as this could make that loss of data permanent.
+
+
+Complete Incompatibility
+------------------------
+
+When Blender switches to a new major version release (e.g. from 3.x to 4.0), there can also be major
+changes that will make the blend-file fully incompatible with older versions of Blender.
+
+In such cases, older Blender will fail opening (or appending/linking from) the newer blend-file, with a
+message stating which minimal version is needed to open it.
+
+In such cases, the last LTS release of the previous release cycle will be kept compatible with the newer
+file format version, and will be usable as converter between both versions.
+
+For example, Blender 3.6LTS can open files from Blender 4.x, and will perform the necessary conversion
+such that when re-saved from 3.6, the files become compatible with all 3.x Blender versions.

manual/files/blend/index.rst

@@ -7,6 +7,7 @@
    :maxdepth: 2
 
    open_save.rst
+   compatibility.rst
    packed_data.rst
    previews.rst
    rename.rst

manual/files/linked_libraries/link_append.rst

@@ -11,6 +11,10 @@ Newly added collections types are available in :menuselection:`Add --> Collectio
 
 Look in the *Outliner*, with display mode set to *Blender File*, to see all your linked and appended data-blocks.
 
+.. note::
+
+   It is not possible to Append or Link data from :doc:`much newer blend-files </files/blend/compatibility>`
+
 
 .. _bpy.ops.wm.link: