I'd like to request the option to have the ability to handle the user editing a cell and then clicking on the ellipsis button without triggering the AfterCommitEdit event.

In my use case the user is entering a code from another table. The ellipsis button is there to show the list of valid values to the user. Because there can be a large number of values, a drop down isn't a good choice. I'd like to allow the user to enter in a partial match and then click the button to show the valid list of values. Then the user can select a valid choice from the list which is pushed into the cell being edited.

It allows me to validate the input in the AfterCommitEdit event.

Currently, if the user is editing the cell and clicks the button, the AfterCommitEdit event is fired and I don't have a way to determine why the ACE event was invoked.

Maybe an event called CellEditingEllipsisButtonClick?

Or, if I'm not using the existing events correctly, I'm open to changing my code around.

An interesting option, but the AfterCommitEdit event must be triggered when cell edit is finished. That's the original purpose of this event.

If you check the entered value, then perhaps BeforeCommitEdit will work better for you. AfterCommitEdit is triggered AFTER finishing editing when you do not have any ability to reject the entered cell value. BeforeCommitEdit allows you to stay in edit mode if required (i.e. if the entered value is incorrect).

If you want to know whether the user clicked the cell ellipsis button at the moment when the BeforeCommitEdit/AfterCommitEdit event is triggered, you can try to track that in with the CellMouseMove event. Its event arguments provide the ElemControl field that can be used to know what elementary cell control like ellipsis button is under the mouse pointer.