4.6 bullet 1 - impossible if app does not support track changes

4.6 first bullet: This is impossible for an implementation that does not
support change tracking. If in such an implementation a user inserts
text in an previously inserted (and tracked) text section, it will have
effectively changed the tracking information since the newly inserted
text has suddenly become part of the earlier insertion. (The
change-tracking information only inserts start and end marker but does
not remember the text. In fact it stores no info that would enable it ti
discover the change.) So at a minimum the part "even if the ...tracking"
should be stricken.