code: func (b *Box) SetResolver(file string, res resolver.Resolver) {
  	d := filepath.Dir(file)
  	b.dirs.Store(d, true)
  	plog.Debug(b, "SetResolver", "file", file, "resolver", fmt.Sprintf("%T", res))
  	b.resolvers.Store(resolver.Key(file), res)
  }
docs: // SetResolver allows for the use of a custom resolver for
  // the specified file