When the command is invoked without any flags, for each deferred transaction the information about its size, initiator object, and flags as well as a human-readable type of the transaction - such as "read" or "write" - are reported.
When the command is invoked with the -chains flag, more detailed information about deferred transactions is shown. The Transaction Chaining section in Model Builder User's Guide explains that in order to append atoms to an existing transaction two or more transactions can be chained together into a linked list with the help of the prev field in the transaction_t type. Passing the -chains flag makes the command show information about all transactions that are linked to each deferred transaction.
When the -show-only-waited flag is passed, the command reports information only about deferred transactions whose completion is waited for via the call to the SIM_transaction_wait function.
Without any flags given, the return value is a list of lists of transaction data, where each data list contains the transaction size, initiator (or NIL if no initiator), the value of the transaction's flags and a human-readable type string describing the type of the transaction.
If the -chains flag is given, the return value is a list of lists of data for each transaction chain record, where each data list contains the ID, the owner, ID of the previous record in the chain, and the state.