来历：qname是qualified name的简写
构成：由名字空间(namespace)前缀(prefix)以及冒号(:),还有一个元素名称构成
URI references can contain characters not allowed in names, and are often inconveniently long, so expanded names are not used directly to name elements and attributes in XML documents.Instead qualified names are used.[Definition: A qualified name is a name subject to namespace interpretation.] In documents conforming to this specification, element and attribute names appear as qualified names.Syntactically, they are either prefixed names or unprefixed names.
QName有两种，一种带前缀的，一种不带前缀的。QName是特定格式的xml元素。
<beans xmlns="http://www.springframework.org/schema/beans"
xmlns:context="http://www.springframework.org/schema/context">
<context:annotation-config />
</beans>
beans就是不带前缀的，namespace为
http://www.springframework.org/schema/beans ，
context就是前缀，元素名称为annotation-config，
namespace为http://www.springframework.org/schema/context
