I get to the right area with this
"../array[@key='header']/map/string[@key='key']" I'm stuck on how to
now match the value "Content-Type" and then findB  the content of
<string key="value">application/x-www-form-urlencoded</string>

B  ../array[@key='header']/map[string[@key='key'][. =
'Content-Type']]/string[@key = 'value']