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It's the same as you can use in Eikon Excel. You can view the explanation in Eikon Excel Formula Builder or in Data Item Browser app in Eikon by clicking on the question mark icon next to a date field in the Parameters tab. Here's the screenshot.
Missing datas with two dates (EDate, SDate)
Get intraday BID/ASK data through ek.get_data
python eikon API - is there a parameter value for Edate which will get "all" the available history?
What other parameters can be used with the statement pertaining to Corporate Actions data such as Stock Splits?
Earnings Announcement dates closing price for company