bug#64960: Documentation for copy-sequence

[Drew Adams]

> > It is not evident what the meaning of "shared" means ?  If I use a
> > string, I get an exact copy and when I change a single character
> > the newlist is changed,  the original string remains the same.
> > So what is shared exactly ?
> 
> A string doesn't share anything because characters are not reference
> values. They are simply copied.

Yes and no.
Chars are not shared, but char properties are.

(setq foo (propertize "abcd" 'p1 t 'p2 42))
;; -> #("abcd" 0 4 (p2 42 p1 t))
(setq bar (copy-sequence foo))
;; -> #("abcd" 0 4 (p1 t p2 42))
(aset foo 1 ?W) ; -> ?W, aka 87
foo ; -> #("aWcd" 0 4 (p2 42 p1 t))
bar ; -> #("abcd" 0 4 (p1 t p2 42))