Fires when the children collection of this 
C1TextElement changes.
The event handler receives an argument of type System.Collections.Specialized.NotifyCollectionChangedEventArgs containing data related to this event. The following NotifyCollectionChangedEventArgs properties provide information specific to this event.
| Property | Description | 
|---|
| Action | Gets the description of the action that caused the event. | 
| NewItems | Gets the items affected by an action. | 
| NewStartingIndex | Gets the index at which the change occurred. | 
| OldItems | Gets the item affected by a System.Collections.Specialized.NotifyCollectionChangedAction.Replace or System.Collections.Specialized.NotifyCollectionChangedAction.Remove action. | 
| OldStartingIndex | Gets the index at which the change occurred for a System.Collections.Specialized.NotifyCollectionChangedAction.Replace or System.Collections.Specialized.NotifyCollectionChangedAction.Remove action. |