Headers | Force.com REST API Developer Guide

Assignment Rule Header
The Assignment Rule header is a request header applied when creating or updating Cases or Leads. If enabled, the active assignment rules are used. If disabled, the active assignment rules are not applied. If a valid AssignmentRule ID is provided, the AssignmentRule is applied. If the header is not provided with a request, REST API defaults to using the active assignment rules.

Call Options Header
Specifies the client-specific options when accessing REST API resources. For example, you can write client code that ignores namespace prefixes by specifying the prefix in the call options header.

Limit Info Header
This response header is returned in each request to the REST API. You can use the information to monitor API limits.

Package Version Header
Specifies the version of each package referenced by a client. A package version is a number that identifies the set of components and behavior contained in a package. This header can also be used to specify a package version when making calls to an Apex REST web service.

Query Options Header
Specifies options used in a query, such as the query results batch size. Use this request header with the Query resource.