Where is the code for combo box plus check box in adempiere multiwindow?

Where is the code for combo box plus check box in adempiere multiwindow? View the picture in the link. Where is the code for this in adempiere classes? I have already checked on APanel, VPanel, CPanel, AWindow, CTable, GridController, VInOutGen, VGenPanel, MiniTable, etc. I couldn't find the appropriate code.

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Its helpful for mixed combobox n check box combination.