<subtitle>Second Edition</subtitle>
<author>Eric A. Meyer</author>
<publisher>O’Reilly and Associates</publisher>
<pubdate>2004</pubdate>
<isbn>blahblahblah</isbn>
</book>
<book>
<maintitle>CSS2 Pocket Reference</maintitle>
<author>Eric A. Meyer</author>
<publisher>O’Reilly and Associates</publisher>
<pubdate>2004</pubdate>
<isbn>blahblahblah</isbn>
</book>
默认的显示：
用css来定义显示层次：
book, maintitle, subtitle, author, isbn {display: block;}
publisher, pubdate {display: inline;}
现在显示：
能够影响显示角色display roles 的特性是css在多种情况下高度有用的重要原因。
