I'm confused about what this would do and why it's needed.

Can you link the mail that you refer to?

(In reply to Ryan Lortie (desrt) from comment #1)
> I'm confused about what this would do and why it's needed.
> 
> Can you link the mail that you refer to?

Actually the mail was to Lars Uebernickel. Here it is, along with his reply:

> On Mon, Oct 20, 2014, at 15:54, Yves-Alexis Perez wrote:
> > Hi,
> > 
> > I'm the maintainer of lightdm and Xfce in Debian, and I recently noted
> > the support for XDG_CURRENT_DESKTOP and DesktopNames property in GDM [1]
> > 
> > LightDM previously used X-LightDM-DesktopName and now switched to
> > DesktopNames, but it seems that this key is not yet present in the
> > latest Desktop Entry Specification [2]. Is the addition planned?

> Ah thanks, I guess you're right. Can you please file a bug about that
> and assign me or Ryan Lortie.

> > [1] https://bugzilla.gnome.org/show_bug.cgi?id=727546
> > [2] http://standards.freedesktop.org/desktop-entry-spec/desktop-entry-spec-latest.html#recognized-keys

Hi -- sorry about the delay in replying; my email has been messed up with respect to freedesktop bugs for the past while.

I think the confusion here is that xsession files are not *really* desktop files, but another type of file.

The question is then where this file format is documented, and the answer currently appears to be "nowhere".  hrmph.

(In reply to Ryan Lortie (desrt) from comment #3)
> Hi -- sorry about the delay in replying; my email has been messed up with
> respect to freedesktop bugs for the past while.
> 
> I think the confusion here is that xsession files are not *really* desktop
> files, but another type of file.
> 
> The question is then where this file format is documented, and the answer
> currently appears to be "nowhere".  hrmph.

And would it hurt to still add it to the desktop spec?

(In reply to Yves-Alexis from comment #4)
> And would it hurt to still add it to the desktop spec?

Being that this key has no place in a desktop file, I'd say that it would be bad to add it to the spec.

okay, here's the plan:

We can document this, not as a proper key, but as an extra paragraph under the OnlyShowIn key.  The desktop file already acts as the "home" of XDG_CURRENT_DESKTOP, so why not explain how we expect this variable to get set?

Created attachment 113899 [details] [review]
desktop-entry-spec: document DesktopNames

Document the DesktopNames key as the mechanism by which
the XDG_CURRENT_DESKTOP environment variable is expected to be set.

We don't document this as a key in the normal way, because it is not a
valid key for desktop files.  We only include a mention of it here
because the desktop entry spec is more or less the "home" of what
XDG_CURRENT_DESKTOP means, and the mechanism by which it is normally set
should be part of that definition.

Comment on attachment 113899 [details] [review]
desktop-entry-spec: document DesktopNames

Review of attachment 113899 [details] [review]:
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Looks good to me. Thanks!

Okay.  Pushed.