Since PHP 5.1.0, every such release has included a migration appendix / upgrade guide. This involves the following:

• php-src/README.UPDATE_X_Y (Examples: 5.1, 5.2)
• phpdoc/appendix/migrationXY.xml (Examples: 5.2, 5.2)

Currently the internals team has created the README files, but this may change.

Some extensions may have been moved to PECL, became bundled, were re-categorized, etc. This information should be updated at this time, or at any time before:

• The XML: phpdoc/en/appendices/extensions.xml
• The script that updates it: phpdoc/scripts.extensions.xml.php

NOTE: This information comes from the comments found within (on top of) every book.xml. Status, and Membership. The Purpose dictates how the extensions are categorized in the index/table of contents.