This is outdated documentation made for eZ Publish Platform 5.1. It is being moved into the eZ Publish 5.x documentation, so please go there for most up-to-date documentation.
Error handling in our REST API is fully based on HTTP error codes. As a web developer, you are familiar with the most common ones: 401 Unauthorized, 404 Not Found or 500 Internal Server Error. The REST API uses those, along with a few more, to provide error handling.