Load node's content from XML according to attribute's value

[#1]

Hi

I'm trying to load XML contents (firstName, familyName) only if (extension="cip12").

code:

.

.

.

<id extension="cip12" root="2.16.724"/>

     <Man>

          <name>

               <given>firstName</given>

               <family>familyName</family>

          </name>

     <Man>

......

.....

How can I do that?