ICU-5681 Add documentation

X-SVN-Rev: 21677

icu4j/src/com/ibm/icu/charset/CharsetUTF8.java

@@ -366,6 +366,13 @@ donefornow:
     }
 }
 
+/*
+ * The purpose of this class is to set isCESU8 to true in the super class,
+ * and to allow the Charset framework to open the variant UTF-8 converter
+ * without extra setup work.
+ * CESU-8 encodes/decodes supplementary characters as 6 bytes instead of the
+ * proper 4 bytes.
+ */
 class CharsetCESU8 extends CharsetUTF8 {
     public CharsetCESU8(String icuCanonicalName, String javaCanonicalName, String[] aliases){
         super(icuCanonicalName, javaCanonicalName, aliases);