--- a/mercurial/helptext/rust.txt	Wed Nov 20 06:32:35 2024 +0100
+++ b/mercurial/helptext/rust.txt	Wed Nov 20 06:33:43 2024 +0100
@@ -1,6 +1,23 @@
 Mercurial can be augmented with Rust extensions for speeding up certain
 operations.
 
+Word of Caution
+===============
+
+Using the Rust extension might result in the use of various repository formats
+that are not supported by non-Rust mercurial. When using a Mercurial
+without Rust support on the same repositories, you might need to downgrade your
+repository formats and/or activate cripplingly slow paths for compatibility.
+For details, see:
+
+    - :hg:`help config.format.use-persistent-nodemap`
+    - :hg:`help config.format.use-dirstate-v2`
+
+In addition, while the tests are run with the Rust code, there might be
+subtle undetected divergences from the historical non-Rust code. So keep
+your eyes open and report any oddity. Rust is not considered a first class
+citizen to the project yet.
+
 Compatibility
 =============
 
@@ -9,6 +26,9 @@
 mileage may vary, but by all means do give us feedback or signal your interest
 for better support.
 
+For compatibility with non-Rust version of Mercurial check the previous "Word of
+Caution" section.
+
 No Rust extensions are available for Windows at this time.
 
 Features