表单控件中textarea标签的特性值有哪些呢？

<input id="btn1" type="button" value="禁用">
<input id="btn2" type="button" value="启用">
<input id="btn3" type="button" value="只读">
<input id="btn4" type="button" value="读写">
<textarea id="test">测试内容</textarea>
<script>
    btn1.onclick = function(){
        test.setAttribute('disabled','');
    };
    btn2.onclick = function(){
        test.removeAttribute('disabled');
    };    
    btn3.onclick = function(){
        test.setAttribute('readonly','readonly');
    };
    btn4.onclick = function(){
        test.removeAttribute('readonly');
    };
</script>