可以将文章内容翻译成中文,广告屏蔽插件可能会导致该功能失效(如失效，请关闭广告屏蔽插件后再试):

问题:

In what order are elements with a tabindex value of 0 focused when the web page is tabbed?

回答1:

The HTML specification states:

Elements that have identical tabindex values should be navigated in the order they appear in the character stream.

回答2:

tabindex assignments are handled the following way (for elements that support the tabindex attribute):

Positive numbers (1,2,3...32767) are handled in tab order.
0 is handled in source order (the order it appears in the DOM)
-1 is ignored during tabbing but is focusable.

This information is taken from : http://www.w3.org/TR/html401/interact/forms.html#adef-tabindex

回答3:

It's a bit more complicated than Alan Haggai Alavi's answer.

After parsing, IE8 and Opera do as the HTML4 spec says. Firefox and Chrome however use DOM order. This matters with malformed markup like this.

<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd">
<html>
  <head>
    <title>Test case 1</title>
  </head>
  <body>
    <form>
      <table>
        <tr><td><input id="first" value="first in the character stream" tabindex="0"></td></tr>
        <div><input id="second" value="second in the character stream" tabindex="0"></div>
      </table>
    <form>
  </body>
</html>

You might well argue that with malformed mark-up all bets are off anyway, so what about JavaScript?

Consider this case:

<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd">
<html>
  <head>
    <title>Test case 2</title>
    <script type="text/javascript">
      moveFirst = function()
      {
        var f = document.getElementById("first");
        f.parentNode.removeChild(f);
        document.body.appendChild(f);
      }
    </script>
  </head>
  <body>
    <form>
      <table>
        <tr><td><input id="first" value="first in the character stream" tabindex="0"></td></tr>
        <tr><td><div><input id="second" value="second in the character stream" tabindex="0"></div></td></tr>
      </table>
    <form>
    <div onclick="moveFirst()">move</div>
  </body>
</html>

In this case, when a user clicks on "move", IE8, Firefox, Chrome and Opera all use DOM order, not character stream order.

Finally HTML5 offers pretty much no guarantees about the tab order between elements that have a tabindex of 0, merely stating that it should follow platform conventions.

回答4:

An example is the best way to remember.

Assume you are pressing Tab key on the keyboard

<button tabindex="0">one</button>
<button tabindex="-1">two</button>
<button tabindex="0">three</button>
<button tabindex="5">four</button>

First four will be focused during Tab press (because tabindex is highest)
then one (because tabindex is 0, next highest, but 1st displayed in the document)
then three (because tabindex is 0, same as above, but 2nd displayed in the document)
then nothing else (The two is never focused because tabindex is -1)

Why is tabindex="0" required? anyway tab stops at a button, right?
True, you can also have tab stop for a div, like: