1. Introduction

This document specifies additional HTTP [RFC2616] status codes for a variety of common situations, to improve interoperability and avoid confusion when other, less precise status codes are used.

Note that these status codes are optional; servers cannot be required to support them. However, because clients will treat unknown status codes as a generic error of the same class (e.g., 499 is treated as 400 if it is not recognized), they can be safely deployed by existing servers (see [RFC2616] Section 6.1.1 for more information).