Returns the index of the first line after the currently visible one. If the
return value is $0$ it means that no lines are currently shown (which only
happens if the control is empty). Note that the index returned by this method
Returns the index of the first line after the currently visible one. If the
return value is $0$ it means that no lines are currently shown (which only
happens if the control is empty). Note that the index returned by this method