rng-preferred-prefix-alist

rng-preferred-prefix-alist is a variable defined in `rng-nxml.el'.
Its value is

(("http://www.w3.org/1999/XSL/Transform" . "xsl")
 ("http://www.w3.org/1999/02/22-rdf-syntax-ns#" . "rdf")
 ("http://www.w3.org/1999/xlink" . "xlink")
 ("http://www.w3.org/2001/XmlSchema" . "xsd")
 ("http://www.w3.org/2001/XMLSchema-instance" . "xsi")
 ("http://purl.org/dc/elements/1.1/" . "dc")
 ("http://purl.org/dc/terms/" . "dcterms"))

Documentation:
Alist of namespaces vs preferred prefixes.

You can customize this variable.