Add comment about CJK compatibility ideographs to DoNotEmit.txt

unicodetools/data/ucd/dev/DoNotEmit.txt

@@ -1,5 +1,5 @@
 # DoNotEmit-17.0.0.txt
-# Date: 2025-07-30
+# Date: 2025-08-04
 # © 2025 Unicode®, Inc.
 # Unicode and the Unicode Logo are registered trademarks of Unicode, Inc. in the U.S. and other countries.
 # For terms of use and license, see https://www.unicode.org/terms_of_use.html
@@ -42,6 +42,14 @@
 # Sequences for Egyptian Hieroglyphs are not listed here. See
 # the kEH_AltSeq property in UAX #57 for that information.
 #
+# CJK compatibility ideographs are not listed here either. Each CJK
+# compatibility ideograph is canonically equivalent to a CJK unified
+# ideograph, which means that distinctions would be lost in normalization.
+# The preferred form for applications that intend to keep the distinction is
+# using a standardized variation sequence instead of a CJK compatibility
+# ideograph. For a comprehensive list of such sequences, see the section
+# "CJK compatibility ideographs" in StandardizedVariants.txt.
+#
 # Note that some sequences could be considered recursive, in the way that
 # the preferred sequence to use may be a subsequence of the "Do Not Emit"
 # sequence. This may have implications for some implementations who may want