New features
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Migrating from PHP 5.4.x to PHP 5.5.x
PHP Manual

## Deprecated features in PHP 5.5.x

### ext/mysql deprecation

The original MySQL extension is now deprecated, and will generate `E_DEPRECATED` errors when connecting to a database. Instead, use the MySQLi or PDO_MySQL extensions.

### preg_replace() /e modifier

The preg_replace() /e modifier is now deprecated. Instead, use the preg_replace_callback() function.

### intl deprecations

IntlDateFormatter::setTimeZoneID() and datefmt_set_timezone_id() are now deprecated. Instead, use the IntlDateFormatter::setTimeZone() method and datefmt_set_timezone() function, respectively.

### mcrypt deprecations

The following functions have been deprecated:

- mcrypt_cbc()
- mcrypt_cfb()
- mcrypt_ecb()
- mcrypt_ofb()

New features
Changed Functions
Migrating from PHP 5.4.x to PHP 5.5.x
PHP Manual