This PHP file describes all the material of your game.

This file is include by the constructor of your main game logic (yourgame.game.php), and then the variables defined here are accessible everywhere in your game logic file.

Using material.inc.php makes your PHP logic file smaller and clean.

Example from "Hearts": if you define this in material.inc.php:

$this->colors = array(
    1 => array( 'name' => clienttranslate('spade'),
                'nametr' => self::_('spade') ),
    2 => array( 'name' => clienttranslate('heart'),
                'nametr' => self::_('heart') ),
    3 => array( 'name' => clienttranslate('club'),
                'nametr' => self::_('club') ),
    4 => array( 'name' => clienttranslate('diamond'),
                'nametr' => self::_('diamond') )
);

... you can access "$this->colors" everywhere in your PHP game logic file.