Merge pull request #12479 from keymanapp/DavidLRowe-kmx-plus-update

docs(core): Update kmx-plus-file-format.md

docs/file-formats/kmx-plus-file-format.md

@@ -35,7 +35,9 @@ Draft spec PR: <https://github.com/unicode-org/cldr/pull/1847>
 - Other than the `sect` table itself, the rest of the sections follow in binary
   order in the file.  In other words, the binary ordering of the section
   identifiers determines the order of the file layout.
-- All sections other than the `sect` table are optional
+- All sections other than the `sect` table are optional for the file 
+  format to be valid, however, a valid keyboard will need most or 
+  all of the sections present to be usable.
 
 ### C7043.2.1 `sect`—Section Table of contents