HHH-16160 Fix some XML related issues that came up

Author: beikov

migration-guide.adoc

@@ -315,10 +315,10 @@ The default precision for SQL Server timestamps was changed to 7 i.e. 100 nanose
 
 Note that these changes only affect DDL generation.
 
-[[array-mapping-changes-on-db2-sap-hana-and-sybase-ase]]
-== Array mapping changes on DB2, SAP HANA and Sybase ASE
+[[array-mapping-changes-on-db2-sap-hana-sql-server-and-sybase-ase]]
+== Array mapping changes on DB2, SAP HANA, SQL Server and Sybase ASE
 
-On DB2, SAP HANA and Sybase ASE, basic arrays now map to the `SqlTypes.XML_ARRAY` type code,
+On DB2, SAP HANA, SQL Server and Sybase ASE, basic arrays now map to the `SqlTypes.XML_ARRAY` type code,
 whereas previously, the dialect mapped arrays to `SqlTypes.VARBINARY`.
 The `SqlTypes.XML_ARRAY` type uses the `xml` DDL type which enables using arrays in other features through the various XML functions.
 
@@ -338,6 +338,19 @@ The migration requires to read data and re-save it.
 
 To retain backwards compatibility, configure the setting `hibernate.type.preferred_array_jdbc_type` to `VARBINARY`.
 
+[[xml-format-mapper-changes]]
+== XML FormatMapper changes
+
+Previous versions of Hibernate ORM used an undefined/provider-specific format for serialization/deserialization of
+collections, maps and byte arrays to/from XML, which is not portable.
+
+XML FormatMapper implementations were changed to now use a portable format for collections, maps and byte arrays.
+This change is necessary to allow mapping basic arrays as `SqlTypes.XML_ARRAY`.
+
+The migration requires to read data and re-save it.
+
+To retain backwards compatibility, configure the setting `hibernate.type.xml_format_mapper.legacy_format` to `true`.
+
 [[sf-name]]
 == SessionFactory Name (and JNDI)