PLPGSQL function schema or table parameter

Is it possible to pass a table name and/or schema name to a plpgsql
function?
How can I use them in the code? Which Types to use for each of the
parameters?

E.g.

create or replace function MyTest (mySchema WhichType?, myTable
WhichType?) returns integer as '

declare result integer;

Begin
      select id into result from mySchema.myTable where...
      return result;
End;
' language plpgsql;

Sorry if this issue has already been addressed before but I can't find
any objective comments on this.
Thanks.
sidnei