Checking for E_STRICT
What has changed in PHP 5.0.x
Appendices
PHP Manual

# Migrating from PHP 4 to PHP 5.0.x

Table of Contents

- What has changed in PHP 5.0.x
- Backward Incompatible Changes
- CLI and CGI
- Migrating Configuration Files
- New Functions
- New Directives
- Databases
- New Object Model
- Error Reporting

See also the migration guides for PHP versions 5.1.x, 5.2.x, 5.3.x, 5.4.x and 5.5.x.