Most improvements in PHP 5.2.x have no impact on existing code. There are
a few incompatibilities
and new error messages
that should be considered, and code should be tested before switching PHP
versions in production environments.
If the system is being upgraded from PHP 5.0.x, the manual section titled
Upgrade Notes for PHP 5.1.x
should also be read.
Similarly, if the system is being upgraded from PHP 4, the manual section
titled Migrating from PHP 4 to PHP 5
should be read as well.
