Migrating from PHP 5.3.x to PHP 5.4.x
Backward Incompatible Changes
Migrating from PHP 5.3.x to PHP 5.4.x
PHP Manual

## What has changed in PHP 5.4.x

Most improvements in PHP 5.4.x have no impact on existing code. There are a few incompatibilities and new features that should be considered, and code should be tested before switching PHP versions in production environments.

For systems being upgraded from an older version of PHP, the relevant documentation is available at:

- Upgrade Notes for PHP 5.3.x.
- Upgrade Notes for PHP 5.2.x.
- Upgrade Notes for PHP 5.1.x.
- Migrating from PHP 4 to PHP 5.