The core of PHP 3.0 is a complete rewrite. This section lists these changes in design. Other changes that don't fit in any of the above categories. Please remember that PHP 3.0's core is a complete rewrite, and thus, there may be other undocumented incompatibilities we haven't thought of ourselves. As with expressions, it's impossible to teach OOP in a few lines, and personally I'm unclear as to how useful this would be in day to day scripting.
Objects can reside in arrays, and can contain arrays.
Function pointers are now supported. A perl-like string concatenation operator was added, the '.' operator. It converts both of its arguments to strings, and concatenates them. Use the '.' operator instead. Support for passing function arguments by reference instead of by value has been added.