Gets a list of PostingInstruction objects, whose value_timestamps fall within the requested time window. If a duration is specified in the @requires decorator, the size of the time window will fall within [hook_effective_date - requirement_duration, hook_effective_date]. If a fetcher_id is specified in the postings argument of the @fetch_account_data decorator and passed as an argument in the get_postings function call, then the time window is specified in the definition of the PostingsIntervalFetcher with the specified fetcher_id in the data_fetchers list of the Contract metadata. If no hook decorator is provided and the current hook is pre/post_posting_code, this returns any covering postings of the proposed batch (plus the proposed postings, if include_proposed=True). The default ordering of the list is by value_timestamp; you can order/filter further using the sorted builtin and other builtin mechanisms.