Function isInnerList

http/unstable_structured_fields.ts:416–420

(
  member: Item | InnerList,
)

 * ```
 */
export function isInnerList(
  member: Item | InnerList,
): member is InnerList {
  return "items" in member;
}

// =============================================================================
// Parsing (RFC 9651 Section 4.2)