Undocumented transaction types

Question

While integrating with the Transactions API I noticed the following undocumented types:

• pro_deposit: seems to be equivalent to exchange_deposit
• pro_withdrawal: seems to be equivalent to exchange_withdrawal
• order: similar to a send but tracks a payment to a merchant
• delayed_canceled: not sure what it represents

Can anyone point me to an updated list of transaction types and/or explain what delayed_canceled transactions represent?