some questions on ORDER BY

Hello,

  I have some questions regarding ORDER BY. If we have the following one:
               
              ORDER BY (lang (_:b))
How we can evaluate this and then ordering the set of solutions?

Also if we have:

         ORDER BY (<http://example.org>)
How we can order the results?
What are the semantics of Order Conditions when they don not contain variables 
like the above examples?