anchor.diff:  
   ''''''''''''''''''''''''''''''''''''''''''''''
   class Party #lightgreen {
  +
   }
   note right #lightgray: eventually expect Party\nto also be 1 or 2 dimensions\n(debtor and/or creditor)
   
   Party "\n\n\nbuyer" <-- Invoice
   Party "\n\n\n  seller" <-- Invoice
  +
  +
   
   
   ''''''''''''''''''''''''''''''''''''''''''''''
  
positive.code: IncomingInvoice <-- PaperclipForIncomingInvoice
  
  
  class PaymentLine #lightgray {
  }
  
  
  IncomingInvoice --> "0..* " PaymentLine
  
  OrderItem <-- IncomingInvoiceItem
  
  ''''''''''''''''''''''''''''''''''''''''''''''
  
  
negative.code:     amount: BigDecimal
  }
  
  enum PaymentMethod #cyan  {
      DIRECT_DEBIT,
      BILLING_ACCOUNT,
      BANK_TRANSFER,
      CASH,
      CHEQUE
  }
  
  
  class IncomingInvoice #pink extends Invoice  {
      received: LocalDate
      status
  }
  
  class BankAccount #lightgreen {
  
  }
  
  
  
  class IncomingInvoiceItem #pink  implements FinancialItem  {
  }
  
  
  class OrderItemInvoiceItemLink #pink {
  
  }
  
  IncomingInvoiceItem <--- OrderItemInvoiceItemLink
  OrderItem <--- OrderItemInvoiceItemLink
  
  IncomingInvoice *---> "1..*" IncomingInvoiceItem
  PaymentMethod <--- IncomingInvoice
  
  
  BankAccount <-- IncomingInvoice
  
  
  class Document #lightgreen {
  