The Accept header field is used to specify media types acceptable to the user agent. It has the following syntax:

Accept = 1#(media-range [weight])

The Accept header field value shall be a comma-separated list of one or more media ranges acceptable in the response. See [RFC7231] Section 5.3.2.

A media range is either a media-type or a wildcard. Wildcards use the asterisk ("*") to group media types into ranges, with <type>/* indicating all subtypes of that type, and */* indicating all media types. For example, the media range image/* matches image/jpeg, which is the default media type for the Single Frame Image Resource Category, and text/* matches text/html, which is the default media type for the Text Resource Category. DICOM specifies that the */* media range matches the default media type for the target's Resource Category. If no default media type is defined for a Resource Category, then any media type from the Resource Category is acceptable.

If the response might contain a payload, an Accept header field shall be present in the request.

If the origin server receives a request without an Accept header field, but that might have a response payload, it shall return a 406 (Not Acceptable).

Any Accept header field values, including media type parameters, that are not valid or not supported shall be ignored by the origin server.