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

From: Aaron Reed <aaronr@us.ibm.com>
Date: Wed, 30 Jul 2008 16:51:14 -0500
To: www-forms@w3.org
Message-ID: <g6qnsb$r6b$1@ger.gmane.org>

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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> 
> 
> 
> 
> http://www.bbc.co.uk/
> This e-mail (and any attachments) is confidential and may contain personal views which are not the views of the BBC unless specifically stated.
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> Do not use, copy or disclose the information in any way nor act in reliance on it and notify the sender immediately.
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Received on Wednesday, 30 July 2008 21:56:02 GMT

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