Again, this should be part of the main narrative, as in:

An HTTP request or response consists of a single contiguous sequence of HEADERS frames, zero or more DATA frames, and possibly a second contiguous sequence of HEADERS frames, where the last frame in the sequence bears an END_STREAM flag.  Additional sequences of HEADERS frames MAY be interspersed with these frames, but they carry no significance in HTTP and can be discarded.

And later:
Contiguous sequences of PUSH_PROMISE frames can be interspersed with responses, ...