function checkNull(o,s) {
		if(o.value == "") {
			alert("“" + s + "”" + "不能为空!");
			o.focus();
			return true;
		}else{
			return false;
		}
	}

	function checkSelected(o,num,s) {
		var i = 0;
		for(var j = 0; j < o.length; j++)
			if(o[j].checked)
				i++;
		if(i <= num && i > 0) {
			return false;
		}else{
			var str = "";
			str = "请选择“" + s + "”";
			if(num > 1)
				str = str + "（最多" + num + "项）";
			alert(str);
			o[0].focus();
			return true;
		}
	}


	function checkLength(o,max,s) {
		if(checkNull(o,s)) return true;
		if(o.value.length > max) {
			alert("“" + s + "”" + "的长度不能超过" + max + "个字符，当前长度：" + o.value.length + "。");
			o.focus();
			return true;
		}
		return false;
	}