add a key-value pair
If key is already present it will be appended.
iterate over all key-value pairs
Multiple values for the same key will be joined in the order they were
added by delimiter.
Optionaldelimiter: stringiterate over all key-value pairs
Multiple values for the same key will get iterated in the order they were added.
get the value for a key
If the key is missing, null will be returned, if multiple values for the
key are present, they will be joined be delimiter.
Optionaldelimiter: stringget all values for a key
whether key has any values associated with it
all keys with at least one value
iterate over all values
If a key has multiple values they will be joined by delimiter.
Optionaldelimiter: stringiterate over all values added
class for storing headers parse from MHTML
Tries to somewhat mimic the behavior of the fetch-api Headers object, with some differences, notably that it does no validation.