function getForm() {
		if (window.navigator.appName.toLowerCase().indexOf("microsoft") > -1) 
			return document.event;
		else 
			return document.forms["event"];
  } // getForm
  
  function submit() {
  	getForm().submit();
  	return false;
  }
  
  function setAndSubmit(id, value) {
  	document.getElementById(id).value = value;
  	submit();
  	return false;
  }
    
  function onClickAllCategories() {
 		var allCategs = document.getElementById("allcategories");
 		if (allCategs.checked) {
			var categs = document.getElementsByName("categories");
			for (var i = 0; i < categs.length; i++)
				categs[i].checked = false;
		} // if 
 	} // onChangeAllCategories
      
 	function onChangeCategories() {
 		var allCategs = document.getElementById("allcategories");
		var categs = document.getElementsByName("categories");
		var amount = categs.length;
		var amountChecked = 0;
 		allCategs.checked = false;
		for (var i = 0; i < categs.length; i++) {
			if (categs[i].checked) {
				amountChecked++;
			} // if element is "checked"
		} // for all categories
		if (amountChecked == amount) {
		 	// uncheck all categories and check "all categories" instead
		 	for (var i = 0; i < categs.length; i++)
				categs[i].checked = false;
			allCategs.checked = true;
		} // if all categies are checked
 	} // allCategories