In Scheme, XML is handled with SXML. Another way would be to append the text to a common string.
(get "/xml" #:mime 'xml
(lambda (rc)
(:mime rc '(*TOP* (WEIGHT (@ (unit "pound"))
(NET (@ (certified "certified")) "67")
(GROSS "95"))))))
The rendered result to the client will be:
<WEIGHT unit="pound"> <NET certified="certified">67</NET> <GROSS>95</GROSS> </WEIGHT>