Metadaten lesen und schreiben per Script

Hello Scripters in Bridge - Metadata

I'm looking for a solution to read the following IPTC field:
"http://iptc.org/std/Iptc4xmpCore/1.0/xmlns/", "extDescrAccessibility"

It should be appended to the existing content of the description using a script.

Thank you very much for your help

Tom