What are the differences between PHP1 and newer versions like PHP5 in terms of syntax and functionality?

In PHP5, there have been significant improvements in terms of syntax and functionality compared to PHP1. Some key differences include the introduction of object-oriented programming features, improved error handling mechanisms, better support for XML processing, and enhanced performance through the introduction of Zend Engine 2.

// PHP1 code
$variable = "Hello World";
print $variable;

// PHP5 code
$variable = "Hello World";
echo $variable;