val assoc : Field_name.t -> t -> Field.field listassoc field_name header returns all values associated to field_name (several can exist into a header). It returns order, value and location if it comes from a source.
val remove_assoc : Field_name.t -> t -> tremove_assoc field_name t removes all values associated to field_name.
concat t0 t1 concats t0 with t1 - any field-name existing in both are not deleted/replaced.
val exists : Field_name.t -> t -> boolexists field_name t is true if field_name exists in t.
val add : Field_name.t -> ('a Field.t * 'a) -> t -> tadd field_name (w, v) t adds a new field-name with value v. add does not replace field_name if it already exists into t.
val add_unless_exists : Field_name.t -> ('a Field.t * 'a) -> t -> tadd_unless_exists field_name (w, v) t is a collection of header fields that is the same as t if t already includes field_name, and otherwise is equivalent to add field_name (w, v) t.
val replace : Field_name.t -> ('a Field.t * 'a) -> t -> treplace field_name (w, v) t replaces existing field-name field_name in t by the new value v. If field_name does not exist, it adds it.
val of_list : Field.field list -> tof_list l returns a header from the list l (without location).
val of_list_with_location : Field.field Location.with_location list -> tval to_list_with_location : t -> Field.field Location.with_location listval to_list : t -> Field.field listval empty : tempty is an empty header which does not have any default values.
val content_type : t -> Content_type.tcontent_type header returns Content_type.t of the given header. If it does not exist, it returns Content_type.default.
val content_encoding : t -> Content_encoding.tcontent_encoding header returns Content_encoding.t of the given header. If it does not exist, it returns Content_encoding.default.
val message_id : t -> MessageID.t optionmessage_id header returns a MessageID.t if it exists. Otherwise it returns None.
val length : t -> intlength hdr returns the length of the given header hdr.
module Decoder : sig ... endmodule Encoder : sig ... endval to_stream : t -> unit -> string optionto_stream header returns a stream of the given header which can be used into protocol like SMTP.