code: func (m *Mapper) FieldByName(v reflect.Value, name string) reflect.Value {
  	v = reflect.Indirect(v)
  	mustBe(v, reflect.Struct)
  
  	tm := m.TypeMap(v.Type())
  	fi, ok := tm.Names[name]
  	if !ok {
  		return v
  	}
  	return FieldByIndexes(v, fi.Index)
  }
docs: // FieldByName returns a field by its mapped name as a reflect.Value.
  // Panics if v's Kind is not Struct or v is not Indirectable to a struct Kind.
  // Returns zero Value if the name is not found.