ICU-20284 Updating docs on mutability of currency fraction digits.
diff --git a/icu4c/source/common/unicode/ucurr.h b/icu4c/source/common/unicode/ucurr.h
index b219875..c30eadb 100644
--- a/icu4c/source/common/unicode/ucurr.h
+++ b/icu4c/source/common/unicode/ucurr.h
@@ -208,6 +208,13 @@
* Returns the number of the number of fraction digits that should
* be displayed for the given currency.
* This is equivalent to ucurr_getDefaultFractionDigitsForUsage(currency,UCURR_USAGE_STANDARD,ec);
+ *
+ * Important: The number of fraction digits for a given currency is NOT
+ * guaranteed to be constant across versions of ICU or CLDR. For example,
+ * do NOT use this value as a mechanism for deciding the magnitude used
+ * to store currency values in a database. You should use this value for
+ * display purposes only.
+ *
* @param currency null-terminated 3-letter ISO 4217 code
* @param ec input-output error code
* @return a non-negative number of fraction digits to be
@@ -221,6 +228,13 @@
/**
* Returns the number of the number of fraction digits that should
* be displayed for the given currency with usage.
+ *
+ * Important: The number of fraction digits for a given currency is NOT
+ * guaranteed to be constant across versions of ICU or CLDR. For example,
+ * do NOT use this value as a mechanism for deciding the magnitude used
+ * to store currency values in a database. You should use this value for
+ * display purposes only.
+ *
* @param currency null-terminated 3-letter ISO 4217 code
* @param usage enum usage for the currency
* @param ec input-output error code
diff --git a/icu4j/main/classes/core/src/com/ibm/icu/util/Currency.java b/icu4j/main/classes/core/src/com/ibm/icu/util/Currency.java
index 51bccd5..fe9db84 100644
--- a/icu4j/main/classes/core/src/com/ibm/icu/util/Currency.java
+++ b/icu4j/main/classes/core/src/com/ibm/icu/util/Currency.java
@@ -840,6 +840,13 @@
* Returns the number of the number of fraction digits that should
* be displayed for this currency.
* This is equivalent to getDefaultFractionDigits(CurrencyUsage.STANDARD);
+ *
+ * Important: The number of fraction digits for a given currency is NOT
+ * guaranteed to be constant across versions of ICU or CLDR. For example,
+ * do NOT use this value as a mechanism for deciding the magnitude used
+ * to store currency values in a database. You should use this value for
+ * display purposes only.
+ *
* @return a non-negative number of fraction digits to be
* displayed
* @stable ICU 2.2
@@ -851,6 +858,13 @@
/**
* Returns the number of the number of fraction digits that should
* be displayed for this currency with Usage.
+ *
+ * Important: The number of fraction digits for a given currency is NOT
+ * guaranteed to be constant across versions of ICU or CLDR. For example,
+ * do NOT use this value as a mechanism for deciding the magnitude used
+ * to store currency values in a database. You should use this value for
+ * display purposes only.
+ *
* @param Usage the usage of currency(Standard or Cash)
* @return a non-negative number of fraction digits to be
* displayed
