当涉及到REST API的返回错误时，我正在寻找关于良好实践的指导。我正在开发一个新的API，所以我现在可以把它带到任何方向。目前我的内容类型是XML，但我计划将来支持JSON。

I am now adding some error cases, like for instance a client attempts to add a new resource but has exceeded his storage quota. I am already handling certain error cases with HTTP status codes (401 for authentication, 403 for authorization and 404 for plain bad request URIs). I looked over the blessed HTTP error codes but none of the 400-417 range seems right to report application specific errors. So at first I was tempted to return my application error with 200 OK and a specific XML payload (ie. Pay us more and you'll get the storage you need!) but I stopped to think about it and it seems to soapy (/shrug in horror). Besides it feels like I'm splitting the error responses into distinct cases, as some are http status code driven and other are content driven.

那么行业建议是什么呢?好的实践(请解释为什么!)，并且，从客户端角度来看，REST API中什么样的错误处理可以使客户端代码更容易?