如何检查xml中是否存在元素使用xpath？

下面是我的元素层次结构。如何检查(使用xpath)AttachedXml元素存在于主消费者的CreditReport下

<Consumers xmlns="http://xml.mycompany.com/XMLSchema">
       <Consumer subjectIdentifier="Primary">
          <DataSources>
               <Credit>
                   <CreditReport>
                      <AttachedXml><![CDATA[ blah blah]]>

使用 boolean() XPath function

The boolean function converts its
argument to a boolean as follows:

• a number is true if and only if
  it is neither positive or negative
  zero nor NaN

• a node-set is true if and only if
  it is non-empty

• a string is true if and only if
  its length is non-zero

• an object of a type other than
  the four basic types is converted to a
  boolean in a way that is dependent on
  that type

如果主消费者的CreditReport中有AttachedXml，那么它将返回true()。

boolean(/mc:Consumers
          /mc:Consumer[@subjectIdentifier='Primary']
            //mc:CreditReport/mc:AttachedXml)