There are many references (good books, papers, ...) available that treat global function fields (over finite fields) of one independent variable. To name a few, Stichtenoth's book "Algebraic Function Fields And Codes", Rosen's "Number Theory in Function Fields".
I was wondering if there are out there any references for function fields (in positive characteristic) with imperfect base field? For instance, function fields $F/k$ where $k = \mathbb{F}_q(t_1, \cdots, t_n)$. I am particularly interested in places, valuations, derivations, differentials and residues of differentials associated to such kind of function fields.
As an aside question, 'how much' of the theory from global function fields of one independent variable, for instance as treated in Stichtenoth, can be done with imperfect base field? I realize it might be difficult to answer such a question precisely but if someone could just give a rough idea of what can be done, it would be great.
Thanks.