<mule xmlns="http://www.mulesource.org/schema/mule/core/2.1"
             xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
             xmlns:spring="http://www.springframework.org/schema/beans"
             xmlns:stdio="http://www.mulesource.org/schema/mule/stdio/2.1"
             xmlns:vm="http://www.mulesource.org/schema/mule/vm/2.1"
        xsi:schemaLocation="
             http://www.springframework.org/schema/beans http://www.springframework.org/schema/beans/spring-beans-2.5.xsd
             http://www.mulesource.org/schema/mule/core/2.1 http://www.mulesource.org/schema/mule/core/2.1/mule.xsd
             http://www.mulesource.org/schema/mule/stdio/2.1 http://www.mulesource.org/schema/mule/stdio/2.1/mule-stdio.xsd
             http://www.mulesource.org/schema/mule/vm/2.1 http://www.mulesource.org/schema/mule/vm/2.1/mule-vm.xsd">
mule后面的xmlns等元素都是什么意思