DOCBOOK: Attributes for text direction and language

I'm new to DocBook, so I apologize in advance if someone else has
already asked the following questions; I couldn't find anything about
them in the archive of this list.

1) What is the DocBook equivalent, if any, of the HTML attribute DIR
for specifying in which direction, i.e. left-to-right or right-to-left,
text should be rendered within the containing element?

2) What is the correct way to specify the language used within the
content of a certain element in DocBook *XML*: a) with the LANG
attribute (as in HTML), b) with the LANG and XML:LANG attributes
(as in XHTML 1.0), or c) with the XML:LANG attribute (as in XHTML
1.1)?

Thank you very much in advance.

Tsuguya Sasaki
http://www.ts-cyberia.net/