/**
 * Returns value of selected option in listbox
 * If there is no options selected - returns null.
 * If multiple options selected - returns first.
 */

function selected(sel){
  if(!sel.options){
     return null;
  }
  for(var i = 0; i< sel.options.length; i++){
     if(sel.options[i].selected){
        return sel.options[i].value;
     }
  }

  return null;
}

/**
 * Returns value of checked radiobutton in radiobuttons group
 * If there is no radiobuttons checked - returns null.
 */

function selectedRadio(sel){
  if(!sel){
     return null;
  }
  if(!sel.length){
     if(!sel.checked){
        return null;
     }
     return true;
  }
  for(var i = 0; i< sel.length; i++){
     if(sel[i].checked){
        return sel[i].value;
     }
  }
  return null;
}

/**
 * Returns true if one of options in radiogroup is checked;
 */
function isChecked(sel){
  return selectedRadio(sel) != null;
}