ICU-13596 Clarifying error code type in numfmt.h parse()
diff --git a/icu4c/source/i18n/unicode/numfmt.h b/icu4c/source/i18n/unicode/numfmt.h
index c06f87b..468a822 100644
--- a/icu4c/source/i18n/unicode/numfmt.h
+++ b/icu4c/source/i18n/unicode/numfmt.h
@@ -641,7 +641,9 @@
* @param result Formattable to be set to the parse result.
* If parse fails, return contents are undefined.
* @param status Output parameter set to a failure error code
- * when a failure occurs.
+ * when a failure occurs. The error code when the
+ * string fails to parse is U_INVALID_FORMAT_ERROR,
+ * unless overridden by a subclass.
* @see NumberFormat::isParseIntegerOnly
* @stable ICU 2.0
*/