html5隐藏div，那个visiblty怎么用？写在哪里，是什么意思？

html5隐藏div，那个visiblty怎么用？写在哪里，是什么意思？

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<div style="visibility:hidden" id="dv">1<br>2<br>3<br>4<br>5</div>
<input type="button" value="显示/隐藏DIV" onclick="document.getElementById('dv').style.visibility = document.getElementById('dv').style.visibility=='hidden'?'visible':'hidden'" />
<br>baba

 $("#aa").click(function(){
            $("#bb").css("visibility","hidden");
        });