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RE: XForms, the xf:header and the HTTP Accept header.

From: Philip Fennell <Philip.Fennell@bbc.co.uk>
Date: Thu, 31 Jul 2008 14:41:39 +0100
Message-ID: <FBFAE0E0B37B4148AF77509764D4BC2007B1E658@bbcxues11.national.core.bbc.co.uk>
To: <www-forms@w3.org>

Aaron,

> With your suggestion of allowing only the default accept 
> header (no xf:headers in the xforms document) or xforms 
> author supplied accept header (using xf:headers in the xforms
> document) then you would be requiring the xforms author to 
> completely anticipate other extensions that the browser has 
> installed or the user might lose out.

It took me a couple of times re-reading my previous e-mail to understand
what I think you think I meant, and I believe I understand where I went
wrong.

I shouldn't have implied that when the developer sets replace="all" that
they then set the Accept header to what they believe Firefox normally
uses. What I should have said was that in the replace="all" case, the
developer would not set the Accept header through xf:header which would
allow the associated submission to revert to the 'current' Accept header
(accommodating all current extensions) for a request that will load a
new document.

With that correction to my suggestion in mind, does the use of
replace="instance" and replace="all" respectively allow the developer to
express their intent for XForms and browser related requests and
therefore make the overriding of the accept header a desirable
behaviour?



Regards

Philip Fennell



-----Original Message-----
From: www-forms-request@w3.org [mailto:www-forms-request@w3.org] On
Behalf Of Aaron Reed
Sent: 30 July 2008 22:51
To: www-forms@w3.org
Subject: Re: XForms, the xf:header and the HTTP Accept header.


Hi Philip,

If you are running the xforms processor on a browser that has other
extensions (who may also modify the default accept header) that would
handle the data coming back at least as well if not possibly better than
the xforms processor, then the server should be able to serve the data
back in the more acceptable format.  With your suggestion of allowing
only the default accept header (no xf:headers in the xforms document) or
xforms author supplied accept header (using xf:headers in the xforms
document) then you would be requiring the xforms author to completely
anticipate other extensions that the browser has installed or the user
might lose out.  While this might be ok for some browsers/processors on
some platforms due to the limited number of available options, if the
user wants his xform to run well on all platforms and browsers, that is
asking for a lot of anticipation from the form author.

--Aaron

Philip Fennell wrote:
> Aaron,
> 
>> we must keep in mind that the accept header by default is what the 
>> browser will accept back which is certainly a far greater variety 
>> than the xforms plugin can accept.  And in most case, I'd argue, the 
>> xforms processor has no idea what the user is trying to do so to 
>> automatically limit the user seems the wrong way to
> go.
> 
> Where a submission uses replace="instance", then the developer's 
> intent is that the response is for the XForms processor. Where 
> replace="all" is used, the intent is that the response is being handed

> back to the parent browser and therefore it should be the developer's 
> responsibility to set the Accept header accordingly in these contexts.

> With that in mind, I'd argue that overwriting the accept header should

> be the preferred behaviour as it is possible for the developer to 
> express their intent through the setting of the submission element's
replace attribute.
> 
> 
> Regards
> 
> Philip Fennell
>> XSLT Developer (Content Management Culture)
>>
>> BBC Future Media & Technology
>> Media Village, 201 Wood Lane London W12 7TP
>> BC4 C4, Broadcast Centre
>>
>> T:	0208 0085318
>>
> 
> -----Original Message-----
> From: www-forms-request@w3.org [mailto:www-forms-request@w3.org] On 
> Behalf Of Aaron Reed
> Sent: 29 July 2008 19:13
> To: www-forms@w3.org
> Subject: Re: XForms, the xf:header and the HTTP Accept header.
> 
> 
> Hi,
> 
> Just a FYI to the WG, Mozilla will 'replace' the value of a request 
> header with the value specified in the xf:header if that particular 
> header is only capable of containing one value (for example, the 
> content type header) but will 'append' the value if the header is 
> capable of containing more than one value.
> 
> With regards to Philip's argument that the Accept header should only 
> contain a single media type and that 'Multiple media types suggest 
> that the XForm can accept multiple representations', we must keep in 
> mind that the accept header by default is what the browser will accept

> back which is certainly a far greater variety than the xforms plugin 
> can accept.  And in most case, I'd argue, the xforms processor has no 
> idea what the user is trying to do so to automatically limit the user 
> seems the wrong way to go.  Now, in cases where the instance is being 
> replaced Philip probably has a point.  But in generic post or get 
> submission scenarios it could be that the user might be trying to get 
> out of xforms completely if there is a more appropriate type available

> but is willing to take xforms in a pinch.
> 
> So unless the user has a way to specify his intent (the way he'd do 
> that would be up to this WG), I'd leave it up to the server to serve 
> down the appropriate format given the information available to it.
> 
> --Aaron
> 
> Philip Fennell wrote:
>> The Mozilla XForms plug-in now, via nightly builds, has support for 
>> the xf:header element and its associated attributes and child 
>> elements. With respect to the HTTP Accept header, the Mozilla 
>> implementation appends the value in the XForm to the request header 
>> whilst, for example, the FormsPlayer implementation overwrites the
> existing header.
>> After discussion with Aaron Reed on the dev-tech-xforms mailing list 
>> he suggests that:
>>
>>> Sounds like you have a usecase for the XForms working group to
>> consider. 
>>> Maybe they could put an attribute on the xf:header that says to
>> replace rather than append.
>>
>> For my two-penneth worth, after thinking about this for a bit, due to

>> the nature of an XForms request and the fact that any data bindings 
>> will only be valid for a single representation of the requested 
>> resource, the Accept header should be overridden and therefore only 
>> have a single media type. Multiple media types suggest that the XForm

>> can accept multiple representations which is of course highly unlike.
>> How you decide which headers are overridden and which get appended is

>> an interesting question.
>>
>> Does anyone on this list have an opinion about this?
>>
>>
>> Regards
>>
>> Philip Fennell
>>
>> http://www.bbc.co.uk/
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> 
> 
> 
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Received on Thursday, 31 July 2008 13:42:16 GMT

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