Re: display margins and modifying the buffer

[Richard Stallman]

    > but setting the display property of the overlay to show anything in the
    > margin makes the text covered by the overlay go invisible;

>From the manual:

  If you put such a display specification directly on text in the
buffer, the specified margin display appears @emph{instead of} that
buffer text itself.  To put something in the margin @emph{in
association with} certain buffer text without preventing or altering
the display of that text, put a @code{before-string} property on the
text and put the display specification on the contents of the
before-string.