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RE: [SVGMobile12] namespace events are not qualified?

From: MAHE Vincent RD-TECH-REN <v.mahe@francetelecom.com>
Date: Thu, 26 May 2005 09:21:37 +0200
Message-ID: <B30D6148F304A743A53B9B44751CDB9A02EAAF59@FTRDMEL2.rd.francetelecom.fr>
To: "Jon Ferraiolo" <jon.ferraiolo@adobe.com>, "Mark Birbeck" <mark.birbeck@x-port.net>, "Ola Andersson" <Ola.Andersson@ikivo.com>
Cc: "KONO Masahiko" <kono.masahiko@canon.co.jp>, <www-svg@w3.org>
Since everybody seems to agree on this, has Ola been given an action to update the Tiny spec. accordingly so that it becomes clearer for every developer & implementer which reads the spec. ?
 
Vincent Mahe

________________________________

De : www-svg-request@w3.org [mailto:www-svg-request@w3.org] De la part de Jon Ferraiolo
Envoyé : mercredi 25 mai 2005 02:07
À : Mark Birbeck
Cc : 'KONO Masahiko'; www-svg@w3.org
Objet : RE: [SVGMobile12] namespace events are not qualified?


Mark,
[As usual!] You are absolutely correct in your analysis. Thanks for carefully describing this whole process and how events are now promiscuous (i.e., DOM2Events "click" really means DOM3Events {"*", "click"}). I suggest that the SVG-t 1.2 spec (and also the SVG-Full 1.2 spec) highlight this somehow to make sure implementers and developers don't get confused (as I was).

Also, I think there needs to be some spec changes in section 13.2 [http://www.w3.org/TR/SVGMobile12/interact.html#SVGEvents]. For example, the SVG-t 1.2 spec says:

-------------------------------------- 

*	SVG 1.1 names are all assumed to be in the "http://www.w3.org/2001/xml-events" namespace. This allows SVG 1.1 content (which did not have a notion of namespaced events) to be upwardly compatible with SVG 1.2 (which adds a notion of namespaced events). Therefore, the SVG 1.1 "SVGZoom" event becomes the {"http://www.w3.org/2001/xml-events", "SVGZoom"} event in SVG 1.2. 

--------------------------------------

Based on the promiscuity statements about backwards compatibility with DOM2 Events, I believe the above bullet is wrong. The old "SVGZoom" is really {"*", "SVGZoom"}.

Jon

At 05:26 PM 5/19/2005, Mark Birbeck wrote:


	Hi Jon,
	
	> Very important issue here.
	
	Definitely.
	
	
	>  Thanks for initiating discussion.
	
	Thanks for replying so quickly ;)
	
	
	I said:
	> >             Let's say we register for:
	> >             
	> >                * click
	> >                * ev:click
	> >                * myns:click
	> >                * yourns:click
	> >             
	> >             
	> >             1. If we dispatch the old DOM 2 Event "click", *all* of
	these listeners
	> >                will be triggered.
	
	You replied:
	>       Assuming the ev: is assigned to the XML Events namespace and myns:
	and yourns:
	> are assigned to different namespaces, then, no, if the mouse is clicked,
	then only
	> the event listeners for "click" and "ev:click" would receive the event.
	At least
	> that is my thinking based on studying the DOM3 Events spec which appears
	to retroactively
	> claim that HTML's click event when namespaced becomes ev:click.
	
	No, I'm pretty certain that this is not what happens. As you rightly say,
	the implication of the DOM 3 Events spec is that there is no longer a
	"click" event, but there is now a {"http://www.w3.org/2001/xml-events",
	"click"} event. So far so good.
	
	However, it also says that if the *listener* is registered for an event with
	no namespace (e.g., "click") OR the event generated has no namespace (e.g.,
	{null, "click"}), then the types will match, *regardless* of the namespace
	[1]:
	
	   For compatibility reasons, the dispatching of an event will ignore
	namespace URIs
	   if either the event or the event listener has a null namespace URI.
	
	The Note goes on to describe what this means:
	
	   If a DOM Level 2 event (i.e. with a null namespace URI) is dispatched in
	the DOM
	   tree, all event listeners that match the type will be triggered as
	described in
	   the DOM event flow.
	
	So, say I give you an XBL document to use with your documents, and my
	document is written to use DOM 2 Events. If it dispatches good old-fashioned
	"click", *all* of the following DOM 3 Event listeners will be triggered in
	your document:
	
	   * ev:click
	   * myns:click
	   * yourns:click
	
	as well as any DOM 2 Event listeners waiting for "click". Note that this
	means that it's not enough for you to avoid using type names from the list
	of 'core' events -- the problem is caused by any DOM 2 Event.
	
	So, just so that everything is clear, if you don't mind me
	cutting-and-pasting your words, I would say that when you say this:
	
	  ...if the mouse is clicked, then only the event listeners for "click" and
	  "ev:click" would receive the event...
	
	although it's what we would like, the reality is you can't say "only":
	
	  ...if the mouse is clicked, then the event listeners for "click" and
	  "ev:click" would receive the event, as would any other listener with
	  "*:click"...
	
	
	Next the Note says this:
	
	   If a DOM Level 3 event (i.e. with a namespace URI) is dispatched in the
	DOM tree,
	   all event listeners with the same type and the same or null namespace URI
	will be
	   triggered as described in the DOM event flow.
	
	The consequence of this is that if my XBL object is 'listening' for "click"
	to come from your document, any handlers that I have registered will be
	invoked if my code receives *any* of the following events from your
	document:
	
	   * ev:click
	   * myns:click
	   * yourns:click
	
	as well as the DOM 2 Event "click".
	
	In other words we have {"*", "click"}, if you'll forgive my notation.
	
	        
	>       What I am assuming is that an implementation would create a DOM3
	Event object
	> for all events, whether the event listener uses DOM2 or DOM3 methods. For
	"click"
	> events, the namespaceURI value on the Event object would be set to
	> "http://www.w3.org/2001/xml-events".
	
	In DOM 3 Events-compliant code it would, since you would use initEventNS().
	But sticking with my example, my DOM 2 Event-compliant code will call
	initEvent() on this Event object, thus setting the namespace URI to null. If
	I then call dispatchEvent() on some target node, it would of course
	correctly trigger any listener for "click". But as I've said, it would also
	trigger any other listeners with a type of "click", even if they have
	non-null namespaces.
	
	And further, I'm saying that the "click" listener that you set up to listen
	for this "click" event would also be triggered by an event that was
	initialised with initEventNS() and dispatched as {"myns", "click"}.
	
	To put all of this a different way, it is only fully qualified event names
	(i.e., QNames) that are 100% unambiguous. Any use of unqualified names is
	ambiguous.
	
	[snip]
	
	
	>       Actually, I think it all works nicely if "click" is truly
	equivalenced to
	> "ev:click", meaning that the assumed default namespace for legacy HTML and
	SVG
	> events is "ev:".
	
	But as I've tried to show, this is actually not possible to achieve -- there
	is no way I can see in the DOM Events model to make this kind of
	'equivalence' (unless the core events are in no namespace in both DOM 2
	Events and DOM 3 Events).
	
	
	> I believe that attempting to wildcard "click" to mean everything:click is
	what
	> would cause problems.
	
	Exactly!
	
	
	I have to say, I cannot see how it is possible to say that "click" ==
	"ev:click" if you are allowing DOM 2 Events and DOM 3 Events to co-exist.
	The whole "ignore namespaces" thing is an attempt to solve this problem, but
	as far as I can see it just doesn't work.
	
	(I think there are other problems with DOM 3 Events, but I'll leave those
	for a separate thread.)
	
	Regards,
	
	Mark
	
	[1]
	http://www.w3.org/TR/DOM-Level-3-Events/events.html#Events-dom2-compatibilit
	y
	
	
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	x-port.net Ltd.
	
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Received on Thursday, 26 May 2005 07:23:17 GMT

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