gistfile1

<?php
array(
    'default' => array(
        'type' => 'Segment',
        'options' => array(
            'route' => '/[:controller[/:action]]',
            'constraints' => array(
                'controller' => '[a-zA-Z][a-zA-Z0-9_-]*',
                'action'     => '[a-zA-Z][a-zA-Z0-9_-]*',
            ),
            'defaults' => array(
                'controller' => 'index',
                'action'     => 'index',
                'format'     => 'html',
            )
            'may_terminate'  => true,
            'child_routes'   => array(
                'format' => array(
                    'type' => 'Segment', 
                    'options' => array(
                        'route' => '[.:format]',
                        'constraints' => array(
                            'format' => '(json|html)',
                        ),
                        'defaults' => array(
                            'format' => 'html',
                        )
                    ),
                ),
            ),
        ),
    ),
);