| Value | Meaning |
|---|---|
| REQUEST0 | The HEADERS frame is opening new stream, which is analogous to SYN_STREAM in SPDY. |
| RESPONSE1 | The HEADERS frame is the first response headers, which is analogous to SYN_REPLY in SPDY. |
| PUSH_RESPONSE2 | The HEADERS frame is the first headers sent against reserved stream. |
| HEADERS3 | The HEADERS frame which does not apply for the above categories, which is analogous to HEADERS in SPDY. If non-final response (e.g., status 1xx) is used, final response HEADERS frame will be categorized here. |
The category of HEADERS, which indicates the role of the frame. In HTTP/2 spec, request, response, push response and other arbitrary headers (e.g., trailers) are all called just HEADERS. To give the application the role of incoming HEADERS frame, we define several categories.