code>dstart &hellip; dend</code> of <code>dest</code>
 with the new text from the range <code>start &hellip; end</code>
 of <code>source</code>.  Return the CharSequence that you would
 like to have placed there instead, including an empty string
 if appropriate, or <code>null</code> to accept the original
 replacement.  Be careful to not to reject 0-length replacements,
 as this is what happens when you delete text.  Also beware that
 you should not attempt to make any changes to <code>dest</code>
 from th