Payables Open Interface Tables DISTRIBUTION_LINE_NUMBER

Dears,
Payables User's Guide said the following about the destination of LINE_NUMBER  from the AP_INVOICE_LINES_INTERFACE:
"None. The import program automatically generates the values for AP_INVOICE_DISTRIBUTIONS_ALL. DISTRIBUTION_LINE_NUMBER"

Questions are:

1) In what order does the program generate the values for AP_INVOICE_DISTRIBUTIONS_ALL. DISTRIBUTION_LINE_NUMBER?
2) How to keep ordering of invoice lines according to the original invoice?
 
THANK YOU FOR ANY SUGGESTIONS,