pub fn append(
  form_data: FormData,
  key: String,
  value: String,
) -> FormData

pub fn append_bits(
  form_data: FormData,
  key: String,
  value: BitArray,
) -> FormData

pub fn new() -> FormData

pub fn set(
  form_data: FormData,
  key: String,
  value: String,
) -> FormData

pub fn set_bits(
  form_data: FormData,
  key: String,
  value: BitArray,
) -> FormData