API
TCA form fields may have custom PHP and Javascript evaluation.
TCA form fields may be set to readonly (HTML attribute). TCA fields of type "none" have new rendering options (date and other formats).

Direct mail has been removed from the core.

The current XHTML-DTD setting may be queried via $GLOBALS['TSFE']->xhtmlDoctype.
The function t3lib_div::sysLog() may be used to log errors.

NOTABLE BUG FIXES
Versioning works now with all MySQL versions (3.23.x and higher). The relogin popup on session timeout in the Backend won't appear again after clicking "No" in the dialog. When copying a file into the same folder in the "Filelist" module, it is automatically renamed.
JSMENU, editPanel and feAdmin now works with multi-byte charsets (eg UTF-8).

INSTALLATI
Please make sure you read the RELEASE_NOTES document in the root of the TYPO3 sources for detailed instructions on how to update or install.
TYPO3 4.0 ships with an empty typo3/ext folder. In other words there are no global extensions any more: Some of the former default global extensions are now system extensions, others need to be reinstalled as "local". We strongly advise you to do this before upgrading.
TYPO3 4.0 uses a new localization scheme (typo3conf/l10n/). To install language packs use the extension managers function for translation handling. Go to the module extension manager and choose "Translation handling" from the drop down. Choose the language(s) you want do use in the backend and hit the "save" button. To get the language pack hit the button "Update from repository". The extensions csh_<language> are obsolete now. After having saved the language selection, translations will be fetched automatically when installing extensions.

TYPO3 4.0 doesn't use symbolic links anymore (on Unix systems). Existing symbolic links from index.php to <TYPO3_root>/tslib/index_ts.php must be changed to <TYPO3_src>/index.php (on Unix systems). The symbolic links from nimbus.ttf and vera.ttf to arial.ttf and verdana.ttf have been removed. If you need those fonts, create the links manually (Unix) or copy the fonts (Windows). If any extension still relies on these symbolic links you will have to create them manually.

As usual on an update, you have to run the Database Analyzer from Install Tool. Choose "compare" to update you database scheme. For details on how to install or update TYPO3 in general see [10]. Also make sure you run the Update Wizard (see above) if you want to benefit from all 4.0 features.

On initializing the "Reference Index Table", see the extensions manuals at .

SPECIAL NOTE ON DIRECT MAIL
When upgrading to TYPO3 4.0, users will also need to upgrade to Direct Mail 2.0.
This new version of Direct Mail has a number of new features, among which: dynamic categories stored in a database table, improved support for character sets and transfer encodings, recipients lists built from FE User Groups, additional configuration options, improved return mail analysis and improved plain text rendering. A number of bugs have been corrected and the extension underwent substantial technical changes: removed dependency on Web->Plugin manager, extraction of all extension components from the core of TYPO3, DBAL compliance, localization, contextual help, etc.  

The new version will require a conversion of existing categories defined in Page TSConfig and of all references to these categories in content elements and in FE Users and Addresses records. The Direct Mail extension will include the required conversion function.

This will also imply an upgrade of any categories subscription plugin used in the frontend. New versions of the Direct Mail Subscription (direct_mail_subscription), Front End User Registration (sr_feuser_register) and Email Address Subscription (sr_email_subscribe) will be published to support the new database structure.

For more details please see the Extensions Manuals

[by Thomas Esders, www.typo3.org ]