bug#19471: Emacs can't copy text

[Eli Zaretskii <eliz@gnu.org>]

> From: Stephen Berman <stephen.berman@gmx.net>
> Date: Mon, 04 Jul 2016 11:21:45 +0200
> Cc: Kelly Dean <kelly@prtime.org>, 19471@debbugs.gnu.org
> 
> On Mon, 04 Jul 2016 11:03:39 +0200 Stephen Berman <stephen.berman@gmx.net> wrote:
> 
> > In fact, with text properties instead of overlays, the displayed string
> > is copied (cf. the variable yank-handled-properties), as can be seen by
> > copying the first line below the section title of the above Info node:
> >
> >    When the ‘read-key-sequence’ function reads a key sequence (*note Key
> >
> > "see " is a display text property, but appears when this text is yanked.
> 
> Well, what showed up here as "*note " did appear as "see " when I yanked
> that text into the Message mode buffer...

And that's the crux of the issue, AFAIU: the OP wanted to be able to
copy/paste the display string so that it would be visible even outside
of Emacs, e.g. when sent in an email message or written to a disk
file.  In that case, text properties and overlay properties/strings
behave the same: you lose them.

The fact that text properties are copied with the text, while overlay
strings and properties aren't is the intended behavior, Emacs does
that since the day overlays were introduced.