@hreflang dropped from <a>?

Hello, RDFa TF.

I've been translating various W3C documents into Japanese, and 
maintaining a list of the translations at [1]. And now it uses RDFa for 
storing metadata for each translation and the page itself.

However, when I passed it thorough the W3 Validator I got an error 
saying "@hreflang is not defined." So I read through the DTD and found 
@hreflang is defined for <link>, but not for <a>.

Is there any reason not to have @hreflang for <a>? Since the doc is 
about translations, I'd like to have some language information for both 
the original docs and translations.

[1] http://standards.mitsue.co.jp/resources/w3c/

-- 
Masataka Yakura
<yakura-masataka@mitsue.co.jp>