Several new features have already been documented in the official documentation, others are listed on the wiki in preparation of getting documented. It is imperative that more people join the effort to complete the documentation for PHP 5.3.0.
Please also review the NEWS file.
THIS IS A DEVELOPMENT PREVIEW - DO NOT USE IT IN PRODUCTION!
The purpose of this alpha release is to encourage users to not only actively participate in identifying bugs, but also in ensuring that all new features or necessary backwards compatibility breaks are noted in the documentation. Please report any findings to the QA mailinglist or the bug tracker.
There have been a great number of other additions and improvements since the last alpha, but here is a short overview of the most important changes:
Namespaces (documentation has been updated to the current state)
Rounding behavior ext/msql has been removed, while ext/ereg will now raise E_DEPRECATED notices ext/mhash has been replaced by ext/hash but full BC is maintained
PHP now uses cc as the default compiler, instead of gcc
A number of bug fixes to ext/pdo, ext/soap, the stream layer among others
Several under the hood changes also require in depth testing with existing applications to ensure that any backwards compatibility breaks are minimized.
The current release plan expects a stable release sometime around the end of Q1 2009.