This value set has an inline code system http://hl7.org/fhir/issue-type, which defines the following codes:
| Lvl | Code | Display | Definition | 
| 1 | invalid  | Invalid Content | Content invalid against the Specification or a Profile | 
| 2 |   structure  | Structural Issue | A structural issue in the content such as wrong namespace, or unable to parse the content completely, or invalid json syntax | 
| 2 |   required  | Required element missing | A required element is missing | 
| 2 |   value  | Element value invalid | element value invalid | 
| 2 |   invariant  | Validation rule failed | A content validation rule failed - e.g. a schematron rule | 
| 1 | security  | Security Problem | An authentication/authorization/permissions issueof some kind | 
| 2 |   login  | Login Required | the client needs to initiate an authentication process | 
| 2 |   unknown  | Unknown User | The user or system was not able to be authenticated (either there is no process, or the proferred token is unacceptable) | 
| 2 |   expired  | Session Expired | User session expired; a login may be required | 
| 2 |   forbidden  | Forbidden | The user does not have the rights to perform this action | 
| 2 |   suppressed  | Information  Suppressed | Some information was not or may not have been returned due to business rules, consent or privacy rules, or access permission constraints.  This information may be accessible through alternate processes | 
| 1 | processing  | Processing Failure | Processing issues. These are expected to be final e.g. there is no point resubmitting the same content unchanged | 
| 2 |   not-supported  | Content not supported | The resource or profile is not supported | 
| 2 |   duplicate  | Duplicate | An attempt was made to create a duplicate record | 
| 2 |   not-found  | Not Found | The reference provided was not found. In a pure RESTful environment, this would be an HTTP 404 error, but this code may be used where the content is not found further into the application architecture | 
| 2 |   too-long  | Content Too Long | Provided content is too long (typically, this is a denial of service protection type of error) | 
| 2 |   code-invalid  | Invalid Code | The code or system could not be understood, or it was not valid in the context of a particular ValueSet | 
| 2 |   extension  | Unacceptable Extension | An extension was found that was not acceptable, or that could not be resolved, or a modifierExtension that was not recognised | 
| 2 |   too-costly  | Operation Too Costly | The operation was stopped to protect server resources. E.g. a request for a value set expansion on all of SNOMED CT | 
| 2 |   business-rule  | Business Rule Violation | The content/operation failed to pass some business rule, and so could not proceed | 
| 2 |   conflict  | Edit Version Conflict | content could not be accepted because of an edit conflict (i.e. version aware updates) (In a pure RESTful environment, this would be an HTTP 404 error, but this code may be used where the conflict is discovered further into the application architecture) | 
| 2 |   incomplete  | Incomplete Results | Not all data sources typically accessed could be reached, or responded in time, so the returned information may not be complete | 
| 1 | transient  | Transient Issue | Transient processing issues. The system receiving the error may be able to resubmit the same content once an underlying issue is resolved | 
| 2 |   lock-error  | Lock Error | A resource/record locking failure (usually in an underlying database) | 
| 2 |   no-store  | No Store Available | The persistent store unavailable. E.g. the database is down for maintenance or similar | 
| 2 |   exception  | Exception | An unexpected internal error | 
| 2 |   timeout  | Timeout | An internal timeout occurred | 
| 2 |   throttled  | Throttled | The system is not prepared to handle this request due to load management | 
| 1 | informational  | Informational Note | A message unrelated to the processing success of the completed operation (Examples of the latter include things like reminders of password expiry, system maintenance times, etc.) |