Unicorn: XHTML 1.1 and W3C XHTML 1.0 Appendix C checker

Dear Sir:
I can¹t understand why Unicorn reports Œlang¹ errors when validating my
website for W3C XHTML 1.0 Appendix C, as my site declares XHTML 1.1 DOCTYPE
and conformance.
In XHTML 1.1, only <example xml:lang=¹en¹> is needed, there is no need to
include <lang=¹en¹>, so I think Unicorn shouldn¹t report errors for this.
Sincerely yours,

Ricardo de la Vega Cotarelo
Webmaster, Hipocampo.org