# Migrating to release 3.6

DITA-OT 3.6 includes performance enhancements such as processing in parallel and in memory, support for PDF changebars with Apache™ FOP, and an updated preview of features for the latest draft of the upcoming DITA 2.0 standard, including the `<audio>` and `<video>` elements, and the new emphasis domain.

Note:
This topic provides a summary of changes in DITA-OT 3.6 that may require modifications to custom stylesheets or plug-ins. For more information on changes in this release, see the DITA-OT 3.6 Release Notes.

## Parallel processing

Pre-processing module code can now be run in parallel by setting the parallel parameter to true. The performance benefits this option provides depend heavily on the source file set, the DITA features used in the project, and the computer doing the processing, but under the right circumstances, you may see notable improvements when this option is enabled.

## In-memory processing

DITA-OT 3.6 introduces a new Store API with preview support for in-memory processing. The Cache Store can be activated by setting the store-type parameter to memory. In-memory processing provides performance advantages in I/O bound environments such as cloud computing platforms, where processing time depends primarily on how long it takes to read and write temporary files. For more information, see Store API – Processing in memory.

## Caching DITA class instances

The DITA-OT Java code uses a new caching `DitaClass.getInstance(cls)` factory method rather than generating `DitaClass` instances directly. This allows previously created instances to be re-used, which reduces the number of instances that need to be created.

Important:
Custom plug-ins that use the `DitaClass` constructor in Java code should be updated to use the `getInstance` factory method instead.

## PDF changebars with Apache FOP

For DITA-OT 3.4, the bundled Apache™ Formatting Objects Processor library was upgraded to version 2.4, which included support for changebars, but those features were not yet enabled in DITA-OT 3.4 pending further testing. DITA-OT 3.6 removes the FOP-specific overrides that disabled changebars in earlier versions, allowing the default PDF2 flagging routines to be applied when generating PDFs with FOP. For details, see Generating revision bars.

Plug-ins that implemented custom FOP flagging by overriding the org.dita.pdf2.fop/xsl/fo/flagging_fop.xsl stylesheet in prior versions will need to be updated, as this file is no longer available in DITA-OT 3.6. #3511, #3591

## Dublin Core metadata removed from HTML5

Up to version 3.5, DITA-OT included the Dublin Core Metadata Element Set in both XHTML and HTML5 output. DITA-OT 3.6 no longer generates Dublin Core metadata in HTML5 output.

Tip:
If necessary, the org.dita.html5.dublin-core plug-in can be installed from the plug-in registry at dita-ot.org/plugins to add Dublin Core metadata to HTML5.

To install the plug-in, run the following command:

    dita install org.dita.html5.dublin-core

## Legacy style attributes moved to CSS

Remaining inline style attributes were removed from HTML5 code, which prevented custom plug-ins from overriding the presentation of the corresponding elements, including:

- `<line-through>` and `<overline>` elements
- syntax diagrams
- long quote citations
- Boolean states

These changes move the default presentation rules to CSS to allow users to override these styles in custom stylesheets. The output is visually equivalent to the results generated by previous toolkit versions.

Important:
In publishing environments that do not use the default common CSS files, these styles may need to be implemented in custom stylesheets.

## XSL variable `msgprefix` removed

The `msgprefix` variable (“DOTX”) has been deprecated since DITA-OT 2.3 and is now removed from DITA-OT 3.6. For more information, see Migrating to release 2.3.