When Is "PERIOD_NAME" Attribute in "AP_INVOICE_LINES_ALL" Table Updated?

Summary:

There is "PERIOD_NAME" attribute in "AP_INVOICE_LINES_ALL" table, and it has valies like '2023-07' in "YYYY-MM" format.

Could you pleae let me know

What is "PERIOD_NAME" attribute in "AP_INVOICE_LINES_ALL" table? and How it works?

Also, When is "PERIOD_NAME" updated?

FYI, I can see there are lots of invoice lines with null value in "PERIOD_NAME" attribute.

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