function __construct()
    {
        $this->setCallbacks();
        $this->setCapabilities();
        $this->capabilities['introspection'] = array(
            'specUrl' => 'http://xmlrpc.usefulinc.com/doc/reserved.html',
            'specVersion' => 1
        );
        $this->addCallback(
            'system.methodSignature',
            'this:methodSignature',
            array('array', 'string'),
            'Returns an array describing the return type and required parameters of a method'
        );
        $this->addCallback(
            'system.getCapabilities',
            'this:getCapabilities',
            array('struct'),
            'Returns a struct describing the XML-RPC specifications supported by this server'
        );
        $this->addCallback(
            'system.listMethods',
            'this:listMethods',
            array('array'),
            'Returns an array of available methods on this server'
        );
        $this->addCallback(
            'system.methodHelp',
            'this:methodHelp',
            array('string', 'string'),
            'Returns a documentation string for the specified method'
        );
    }