Comment 22 for bug 510010

From the spec

# Link Types
# Alternative
# Designates substitute versions for the document in which the link occurs.
# When used together with the lang attribute, it implies a translated version
# of the document. When used together with the media attribute, it implies
# a version designed for a different medium (or media).
http://www.w3.org/TR/html4/types.html#type-links