jQuery表单对象属性过滤选择器
<div id="p1" attr="p1"><input type="text" id="in001" value="in001"><input type="text" id="in002" disabled="disabled" value="in002"><input type="checkbox" id="chk001" checked="checked" ><input type="checkbox" id="chk002" ><select id="slt001"><option>11</option></select><select id="slt002" multiple="multiple" size="5" ><option>21</option><option selected="selected">22</option><option>23</option><option selected="selected">24</option><option>25</option></select></div>
注意$(':checked')与$('input:checked')的区别；
