8315064: j.text.ChoiceFormat provides no specification on quoting behavior

Reviewed-by: naoto

src/java.base/share/classes/java/text/ChoiceFormat.java

@@ -187,6 +187,12 @@ import java.util.Arrays;
  *
  * <i>Note:The relation &le; is not equivalent to &lt;&equals;</i>
  *
+ * <p>If a <i>Relation</i> symbol is to be used within a <i>Format</i> pattern,
+ * it must be single quoted. For example,
+ * {@code new ChoiceFormat("1# '#'1 ").format(1)} returns {@code " #1 "}.
+ * Use two single quotes in a row to produce a literal single quote. For example,
+ * {@code new ChoiceFormat("1# ''one'' ").format(1)} returns {@code " 'one' "}.
+ *
  * <p>Below is an example of constructing a ChoiceFormat with a pattern:
  * <blockquote>
  * {@snippet lang=java :