[xsl] problem with json-to-xml()

["Wolfhart Totschnig wolfhart.totschnig@xxxxxxxxxxx" <xsl-list-service@xxxxxxxxxxxxxxxxxxxxxx>]

Hello,

I am using the json-to-xml() function for the first time and cannot get 
it to work. I was hoping that one of you could help me.

I have JSON data stored in a text file called "json". I can transform 
this data into xml and insert it into my output document with

json-to-xml(unparsed-text('json'))

That works as expected. The xml data that is produced from the JSON data 
and inserted into my output document looks like this (abbreviated):

B <map xmlns="http://www.w3.org/2005/xpath-functions";>
B B B B B B B B  <string 
key="@context">http://lobid.org/resources/context.jsonld</string>
B B B B B B B B  <string 
key="id">http://lobid.org/resources/search?q=isbn:3-492-21746-X&amp;format=json</string>
B </map>

Now, what I really would like to add to my output is the value of 
/map/string[@key='id'], that is, 
"http://lobid.org/resources/search?q=isbn:3-492-21746-X&amp;format=json";. 
I thought that it would be as simple as this:

<xsl:value-of 
select="json-to-xml(unparsed-text('json'))/map/string[@key='id']"/>

But this doesn't work. It does not produce any output. What am I 
misunderstanding?

Thanks in advance for your help!

Wolfhart