A-IM
The HTTP A-IM request header is similar to HTTP Accept. However, it limits the changes that can be made to the representation.
Usage
The HTTP A-IM request header is used to indicate the types of content the client can understand and is similar to HTTP Accept in this regard. However, a HTTP response can be the result of several instance manipulations, and the A-IM HTTP header is used to restrict such operations.
HTTP responses that employ more than a single instance manipulation must have them considered and applied in the order in which they appear in the A-IM header.
Example
In this example, the client indicates that it can understand the vcdiff and gzip encodings, although will prefer vcdiff as indicated by the q factor.
A-IM: vcdiff, gzip;q=0.4
Takeaway
The HTTP A-IM request header is similar to HTTP Accept, except that it puts restrictions on the instance manipulations that are allowed in the HTTP response.