function combo_add(id, text, value)
{
  option=document.createElement('OPTION');
  _byID(id).options.add(option);
  option.text = text;
  option.value = value;
}

function combo_delete(id, option_index)
{
  _byID(id).options[option_index]=null;
}

function combo_empty(id)
{
  while(_byID(id).length > 0) combo_delete(id,0);
}

function switch_inputs(show, hide)
{
  _byID(show).style.display = 'block';
  _byID(hide).style.display = 'none';
}