Transaction type
Every entry in the ledger carries a transaction type that says what kind of event it records. The type decides where the entry appears in statements, which references (booking, usage log, expense) it can carry, and whether it is treated as a debit or a credit.
The types Syndik8 writes include: usage charge, event charge, minimum shortfall, periodic dues, maintenance expense, expense credit, payment, reversal, and manual adjustment. Each has a fixed sign convention and a fixed posting trigger — the transaction types reference documents them in full.