Function parseItem

http/unstable_structured_fields.ts:704–715

(input: string)

 * ```
 */
export function parseItem(input: string): Item {
  const state: ParserState = { input, pos: 0 };
  skipSP(state);
  const item = parseItemInternal(state);
  skipSP(state);
  if (!isEof(state)) {
    throw new SyntaxError(
      `Invalid structured field: unexpected character at position ${state.pos}`,
    );
  }
  return item;
}

function parseItemOrInnerList(state: ParserState): Item | InnerList {
  if (peek(state) === "(") {