This code:

public struct Test.Struct {
  Enum a;
}

public enum Test.Enum {
  A, B, C
}

Leads to:

In file included from test.c:2:
test.h:15: error: expected specifier-qualifier-list before 'Enum'
error: cc exited with status 256
Compilation failed: 1 error(s), 0 warning(s)

Because test.h declares Enum after defining Struct.