I had trouble for awhile working with XML in Postman, in particular with scripting out xml calls and parsing them. The company I work at has some legacy web applications (SOAP and SAML), and I was done using the tooling they had, as it was clunky and difficult to use. After much research and testing, I was able to find the Cheerio.js library in postman, and could do all the native xml manipulation I needed, especially making a SAML request to get an Assertion, and use that against a SOAP service. I made a video on it and created some test scripts as resources. Take a look at the video description.
I hope this helps anyone looking for native xml use in postman, especially those who don’t work with JSON based services!