--- a/doc/EFR-testing	Thu Dec 15 02:08:55 2022 +0000
+++ b/doc/EFR-testing	Thu Dec 15 02:18:51 2022 +0000
@@ -12,3 +12,11 @@
 For debugging, we also have gsmefr-cod-parse and gsmefr-dec-parse utilities that
 parse ETSI *.cod and *.dec file formats and dump their content in human-readable
 form similar to gsmrec-dump.
+
+Please note that all ETSI test sequence file formats are endian-dependent: their
+original programs read and write 16-bit words in the local machine's native byte
+order, and whenever you are working with published test sequence files, you have
+to check to see if they are BE or LE.  Our gsmefr-etsi-{enc,dec} and
+gsmefr-{cod,dec}-parse programs support both byte orders; the default is LE
+(matching the main parts of ts_100725v050200p0.zip), or you can select BE with
+-b option.