网页设计 TabIndex元素

<form method="post" action="#">
<p><label for="t1">The first pressing Tab to set focus to textbox </label><input type="text" id="t1" tabindex="1" /></p>
<p><label for="t2">The Second pressing Tab to set focus to textbox </label><input type="text" id="t2" tabindex="2" /></p>
<p><label for="t3">The Third pressing Tab to set focus to textbox </label><input type="text" id="t3" tabindex="3" /></p>
<p>Press Tab, Not focusing to textbox <input type="submit" id="t4" tabindex="-1" value="SendInfo" /></p>
</form>