Specifies the index position
of the first character of the text selection stored in the
during a change event.
A valid integer representing the 0-based
index value of the first character of the text selection.
no text is selected, this property is set to the position of the
text entry cursor at the time the change is made. Changing the value
of this property changes which characters will be replaced by the
value of change and also repositions the text entry cursor.