/// <summary>
/// <para>Shifts forward or backward by *number of letters* specified. If past </para>
/// <para>beginning or end of document,furtherst point possible is returned.</para>
/// </summary>
/// <param name="start">The starting point pointer to shift from</param>
/// <param name="dir">The direction to shift in</param>
/// <param name="numLetters">The number of letters to shift by.</param>
/// <returns></returns>
public static TextPointer LetterShift(this TextPointer start, LogicalDirection dir, uint numLetters)
{
return(start.LetterShift((dir == LogicalDirection.Forward ? (int)numLetters : -(int)numLetters)));
}