Classes and Subclasses
Accounts are organized in classes, subclasses, sub-subclasses, and so on. For example:
Class: 4 - Receivables and Payables
Subclass: 40 - Payables; 41 - Receivables
Sub-subclass: 419 - Advances Received from Customers, Discounts, and Refunds
Sub-sub-subclass: 4191 - Advances Received on Orders