Exported field names inhabit a global namespace but unexported (lower case) field names
belong to the namespace of the package in which they lexically appear.

The "reflect" API doesn't mention this, which can lead to surprising results
when searching for a lowercase field by name.

   func (v Value) FieldByName(name string) Value
   FieldByName returns the struct field with the given name.
   It returns the zero Value if no field was found.
   It panics if v's Kind is not struct.

In the example below, a struct has two fields, both called r, but belonging to different
namespaces.  The "reflect" algorithm, when searching for "r", finds
both, and assumes there's a conflict when in reality there isn't.  Without changing the
existing API, that's the best we can do, but it would be useful to document this because
otherwise the choice of unexported field names inside one package can have subtle
effects on another package using reflection.

http://play.golang.org/p/WTj5d06CQ3

(gri: I know you know all this already.)