code: function(json){
      
      // Protect against forgetting the new keyword when calling the constructor
      if(!(this instanceof FieldValue)){
        return new FieldValue(json);
      }
      
      // If the given object is already an instance then just return it. DON'T copy it.
      if(FieldValue.isInstance(json)){
        return json;
      }
      
      this.init(json);
    }
docs: Information about the value of a field.
  
  @see {@link https://github.com/FamilySearch/gedcomx-record/blob/master/specifications/record-specification.md#field-value-data-type|GEDCOM X Records Spec}
  
  @class FieldValue
  @extends Conclusion
  @param {Object} [json]