docs(cockpit): a held train stays the copy drawn, the read APIs and their exports are experimental, and leaving a view does not track an earlier aircraft again

changelog.d/1686-cockpit-subjects.md

@@ -5,8 +5,8 @@
   exactly on it, and a generic HUD adds source rows, a banner, a veil (off
   under reduced motion) and a bottom progress line. The Rail and Transit
   layers expose read and hold APIs so a selected train or vehicle can be
-  ridden, and `./layers/rail/paths` is exported; `docs/APPLICATION.md` shows
-  a minimal provider. GEV itself registers none, and entry to the built-in
-  aircraft, satellite and vessel views is unchanged; a provider's subject
-  takes entry when it was selected after them (Denis Groshev, @ZloyS,
-  #1686).
+  ridden, and `./layers/rail/paths` is exported; these exports and read APIs
+  are experimental. `docs/APPLICATION.md` shows a minimal provider. GEV
+  itself registers none, and entry to the built-in aircraft, satellite and
+  vessel views is unchanged; a provider's subject takes entry when it was
+  selected after them (Denis Groshev, @ZloyS, #1686).