invoice_collection = "<invoice_collection>"  List_E(invoice) "</invoice_collection>".
invoice = "<invoice>" customer  [annotation] entries "</invoice>".
customer = "<customer>"  List_E(name)  List_E(address) "</customer>".
annotation = "<annotation>" PCDATA_1 "</annotation>".
entries = "<entries>" entry "</entries>".
name = "<name>" PCDATA_2 "</name>".
address = "<address>" PCDATA_3 "</address>".
entry = "<entry>" PCDATA_4 "</entry>".
List_E (S) ~ {S}.
PCDATA_1 = <p> Ident.
PCDATA_2 = <p> Ident.
PCDATA_3 = <p> Ident.
PCDATA_4 = <p> Ident.