bug#14801: 24.3.50; Document monitor attributes (e.g., `workarea' and `mm-size')

[Drew Adams]

> > Monitor attributes are partially documented in `C-h f
> > display-monitor-attributes-list'.  They should also be (fully)
> > documented in the Elisp manual.
> 
> Actually I was preparing for that.

Great.  Thanks for working on it.

> See the bottom of this mail.
> 
> > Even in the doc string of d-m-a-l, the description is incomplete and
> > needs to be filled out.
> 
> > Attribute `workareas' is described only in terms of "the workarea".
> > There is no explanation of what is meant by "workarea" (which should
> > presumably be two words, BTW).
> 
> While I was creating the docstring, I actually looked for the
> definition of "workarea" in EWMH on which the implementation is based.
> Unfortunately, it only says as "work area".
> 
>   http://standards.freedesktop.org/wm-spec/1.3/ar01s03.html#id3075721
> 
> But I've just found the GDK documentation has some explanation: "The
> work area should be considered when positioning menus and similar
> popups, to avoid placing them below panels, docks or other desktop
> components."
> 
>   https://developer.gnome.org/gdk3/3.8/GdkScreen.html#gdk-screen-get-
> monitor-workarea
> 
> If it is allowed to use "panels", "docks" or "desktop components"
> without their definitions, probably similar explanation of "work area"
> can be provided.

Thanks for trying to find out what it is.  I don't understand, myself,
but I'm not going to spend the time necessary to study this.  What you
might want to do, especially if things will remain only partly explained,
is to refer readers to some such external reference for more info.

I had no idea, for example, that this involved something called a work
area that is defined externally (e.g. as part of a standard or similar).
I thought it was just an Emacs thing.  If it is only Emacs then we really
need to specify it.  But if it is defined elsewhere then we can just
summarize and point to the external description for more information.

> > Attribute `mm-size' is described only as "the width and height in
> > millimeters".  It's all very nice to say what the units are, but
> > what is it that is being measured?  The width & height of what?  If
> > it is the "work area" (whatever that might be) then say so
> > explicitly.
> 
> Of the monitor.  I thought it was obvious from the context.  But I can
> add "of the physical monitor" for clarity.

Yes, thanks.

> > Beyond all this, what on Earth IS a monitor "attribute"?  Is it
> > supposed to be the same thing as a frame parameter?
> 
> No.  It is an alist describing some kinds of information about current
> configuration of each physical monitor.  I named it after "file
> attributes".

That's fine.  Please just say that then: it is an alist of...  And
give a little more information to give a better idea.  Just substituting
"some kinds of information" for "attribute" won't get us very far.

> The current draft of the Elisp manual begins like this:
> 
> @node Multiple Physical Monitors
> @section Multiple Physical Monitors
> @cindex multiple physical monitors
> 
>   On some ``multi-monitor'' setups, a single graphical display outputs
> to more than one physical monitor.  You can get some kinds of
> information on each physical monitor to examine the current monitor
> configuration.  Because the monitor configuration can be changed
> dynamically in general, you should avoid reusing the information
> obtained some time ago.
> 
>   Information on each physical monitor is represented as
> ``attributes'', an alist of attribute keys and values as follows:

Sounds better already.  Call them "monitor attributes", to be even
clearer.  Thx.