# Migrating to release 4.0

DITA-OT 4.0 requires Java 17 and includes a new plug-in for easier PDF customization, project file improvements, updates to LwDITA processing, and support for the split chunking feature in the latest draft of the upcoming DITA 2.0 standard.

Note:
This topic provides a summary of changes in DITA-OT 4.0 that may require modifications to custom stylesheets or plug-ins. For more information on changes in this release, see the DITA-OT 4.0 Release Notes.

## DITA-OT now requires Java 17

DITA-OT 4.2 is designed to run on Java version 17 or later and built and tested with the Open Java Development Kit (OpenJDK). Compatible Java distributions are available from multiple sources:

- You can download Oracle distributions from oracle.com/java under commercial license.
- Eclipse Temurin is the free OpenJDK distribution available from adoptium.net.
- Free OpenJDK distributions are also provided by Amazon Corretto, Azul Zulu, and Red Hat.
- Java versions are also available via package managers such as Chocolatey, Homebrew, or SDKMAN!

Note:
The Java virtual machine is generally backwards compatible, so class files built with earlier versions should still run correctly with Java 17 and DITA-OT 4.2. If your DITA-OT installation contains plug-ins with custom Java code, you may need to recompile these with Java 17 — but in most cases, this step should not be necessary.

## Deprecated attribute set reflection in PDF2

The legacy attribute set reflection in PDF2 has been replaced with code that generates new attribute sets directly. This change is backwards-compatible as the old attribute set reflection code has been retained, but PDF2 now uses the new attribute set generation mechanism everywhere reflection was used. Custom plug-ins that still use reflection should be updated to the new approach, as the legacy code may be removed in a future version. #3827, #3829

## Code references now default to UTF-8 encoding

The default character set for code references has been changed from the system default encoding to UTF-8.

This allows a wider range of characters to be used without needing to specify the `@format` attribute on the `<coderef>` element as described in character set definition or change the default encoding in the configuration.properties file. #4046
Note:
If you have code references that require a different encoding, use either of these mechanisms to specify the character set explicitly.

## Deprecated `place-tbl-lbl` template in HTML5

The `place-tbl-lbl` template that was originally used to define table titles in XHTML has been deprecated in HTML5 processing and will be removed in a future release. This template was carried over from XHTML code (which still has a copy that is used), but the copy in HTML5 is not called. #3435, #4056