• PAGE UP: Move to the previous month.
• PAGE DOWN: Move to the next month.
• CTRL + PAGE UP: Move to the previous year.
• CTRL + PAGE DOWN: Move to the next year.
• CTRL + HOME: Open the datepicker if closed.
• CTRL/COMMAND + HOME: Move to the current month.
• CTRL/COMMAND + LEFT: Move to the previous day.
• CTRL/COMMAND + RIGHT: Move to the next day.
• CTRL/COMMAND + UP: Move to the previous week.
• CTRL/COMMAND + DOWN: Move the next week.
• ENTER: Select the focused date.
• CTRL/COMMAND + END: Close the datepicker and erase the date.
• ESCAPE: Close the datepicker without selection.

As u can see two of them are windows default shortcuts (ctrl + pageUp/Down), so its really unlikely for standard users.

Is there any chance to customize it? or some other way, for example setting focus on first element to let it be changed by TAB?