Load content according to sibling attribute from XML

[#1]

Hi

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

code:

.

.

  <human>

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

       <Man>

            <name>

                 <given>firstName</given>

                 <family>familyName</family>

            </name>

       <Man>

  <human>

......

.....

How can I do that?