because recently  RESTful  specification is being followed to write  api  interface, according to the specification, the operation result should be represented by  http  status code, not in the result set: 
{
    code: 200 , 
    msg: "" ,
    ....
}return. Encounter a scene:
some special errors (such as the need for further action based on the specific status code client) need to return an explicit status code rather than the same as a normal error.
  in which interval should a custom  http  status code be defined properly? And will not conflict with predefined or reserved status codes?  
