code: func (sd *structDef) addSingleInheritance(apiDef *raml.APIDefinition, strType string) {
  	// check if parent is user defined type
  	if _, ok := apiDef.Types[strType]; ok {
  		strType = strings.Title(strType)
  	}
  
  	fd := fieldDef{
  		Name:          strType,
  		IsComposition: true,
  	}
  	sd.Fields[strType] = fd
  
  }
docs: // add single inheritance
  // inheritance is implemented as composition
  // spec : http://docs.raml.org/specs/1.0/#raml-10-spec-inheritance-and-specialization