...

• linked requirements may be identified by setting an attribute named "requirement" with the respective issue key at the Test method level, using the ITestResult object"; multiple requirements may be specified by using the space delimeterdelimiter
• the Test to report results against to may be identified by using and attribute named "test";
  
  • if the "Test" attribute is used explicitly, then the Test must exist or else it will not be imported.

...

Notes and Limitations

• attachments (e.g. screenshots and other files) are not supported/imported as they are not embedded in the XML report; there is no official way for referring or embedding attachments (request on GitHub)

References

• http://testng.org/doc/
• https://github.com/cbeust/testng
• http://testng.org/doc/documentation-main.html#logging-xml-reports