New Global Constants
Other changes
Migrating from PHP 5.2.x to PHP 5.3.x
PHP Manual

## Changes to INI file handling

PHP 5.3.0 has significantly improved performance and parsing of INI files, and adds several new syntax features.

- The standard php.ini files have been re-organized and renamed. php.ini-development contains settings recommded for use in development environments. php.ini-production contains settings recommended for use in production environments.
- There is now support for two special sections: [PATH=/opt/httpd/www.example.com/] and [HOST=www.example.com]. Directives set in these sections cannot be overridden by user-defined INI files or at runtime. More information about these sections can be found here.
- zend_extension_debug and zend_extension_ts have been removed. Use the zend_extension directive to load all Zend Extensions.
- zend.ze1_compatibility_mode has been removed. If this INI directive is set to On, an `E_ERROR` error is emitted at startup.
- It is now possible to use the full path to load modules using the "extension" directive.
- "ini-variables" can now be used almost anywhere in a php.ini file.
- Runtime tightening of open_basedir restrictions is now possible.
- It is now possible to use alphanumeric or variable indices in INI option arrays.
- get_cfg_var() is now able to return "array" INI options.
- A new directive, mail.add_x_header, has been added.
- user_ini.filename is new
- user_ini.cache_ttl is also new
- exit_on_timeout is new too
- open_basedir is now PHP_INI_ALL

The following new ini directives have been added:

- user_ini.filename and user_ini.cache_ttl for the new .htaccess-style user INI file mechanism.
- Added mbstring.http_output_conv_mimetype. This directive specifies the regex pattern of content types for which mb_output_handler() is activated.
- Added request_order. Allows controlling which external variables will be available in $_REQUEST.

The following ini directives have new default values:

- session.use_only_cookies is now set to "1" (enabled) by default.
- oci8.default_prefetch has changed from "10" to "100".

New Global Constants
Other changes
Migrating from PHP 5.2.x to PHP 5.3.x
PHP Manual