function echo( txt ) { window.document.writeln( txt ); }

function get_obj_by_id( obj_id ) {
  return window.document.getElementById(obj_id);
}

function set_class( object, class_name ) {
  object.className = class_name;
}

function set_img_src( img_obj, img_src) {
  img_obj.src = img_src;
}

function set_display_hide( object ) {
  object.style.display = 'none';
}

function set_display_visible( object ) {
  object.style.display = 'block';
}

function z_fill( nb ) {
  if ( nb < 10 ) { nb = '000'+nb }
  else if ( nb < 100 ) { nb = '00'+nb }
  else if ( nb < 1000 ) { nb = '0'+nb }
  return nb;
}