When entering text into a TextBox that is not empty, most users expect newly typed characters to be inserted where the cursor is, pushing existing text off to the right. A TextBox with a MaskedEditExtender overwrites existing text instead of inserting.
Example: The textbox currently contains "01/23/1999". The user places the cursor in between the "2" and the "3", presses backspace, and types a "1", expecting the result to be "01/13/1999". Instead, the "1" overwrites the "3", resulting in "01/11/999_".
This new "Insert vs. Overwrite" feature would need to maintain the current default behavior of the MaskedEditExtender so as to not break existing code. I suggest adding a property named NewTextMode to the MaskedEditExtender which could be used to toggle the "Insert" functionality. The possible values for the NewTextMode property would be Overwrite and Insert, and the default value would be Overwrite.
Example: The textbox currently contains "01/23/1999". The user places the cursor in between the "2" and the "3", presses backspace, and types a "1", expecting the result to be "01/13/1999". Instead, the "1" overwrites the "3", resulting in "01/11/999_".
This new "Insert vs. Overwrite" feature would need to maintain the current default behavior of the MaskedEditExtender so as to not break existing code. I suggest adding a property named NewTextMode to the MaskedEditExtender which could be used to toggle the "Insert" functionality. The possible values for the NewTextMode property would be Overwrite and Insert, and the default value would be Overwrite.