activationhook.php

<?php
class MyPlugin {
	static function activation_hook() {
		if ( ! version_compare( PHP_VERSION, '5.3.0', '>=' ) ) {
			deactivate_plugins( __FILE__ );
			wp_die( wp_sprintf( '%1s: ' . __( 'Sorry, This plugin has taken a bold step in requiring PHP 5.3.0+. Your server is currently running PHP %2s, Please bug your host to upgrade to a recent version of PHP which is less bug-prone.', 'myplugin' ), __FILE__ , PHP_VERSION ) );
		}
	}
}
register_activation_hook( __FILE__, array( 'MyPlugin', 'activation_hook' ) );

pregreplacecallback.php

<?php
echo preg_replace_callback( '/^(Hello)\s(\w+)\s(World)$/', function ( $match ) {
	return $match[ 1 ] . ', awesome ' . $match[ 3 ] . '!';
}, 'Hello cruel World' ); // => "Hello, awesome World!"

uasort.php

<?php
uasort( $array, function( $a, $b ) {
	return $a > $b;
});