Fetch.HeadersRequest and response headers.
Warning. We left out mutable operations out of the interface but remember these objects may mutate under your feet.
The type for Headers objects.
mem h hs is true iff header h has a value in hs. The lookup is case insensitive.
find h hs is the value of header h in hs (if any). The lookup is case insensitive.
fold f hs acc folds the headers h of hs and their value v with f h v starting with acc. It's unclear but header names are likely lowercased.
of_obj o uses the keys and values of object o to define headers and their value.
of_assoc ~init assoc are the headers from init (default si empty) to which the header value pairs of assoc are appended. If a header is defined more than once this either overwrites the previous definition, or appends to the value if if the value can be multi-valued.