Custom meta box - Wordpress

    function ominid_blocks_inner_box(){
        echo "Hello world";
    }

    function ominid_blocks_add_custom_box(){
        if(function_exists('add_meta_box')){
            add_meta_box( 'ominid-blocks', 'Bloques', 'ominid_blocks_inner_box', 'page', 'normal', 'high' );
        }
    }

    add_action('admin_menu', 'ominid_blocks_add_custom_box');