W3C home > Mailing lists > Public > public-html@w3.org > February 2009

Re: Need differentiator between "no alt text provided" and "no alt text necessary"

From: Maciej Stachowiak <mjs@apple.com>
Date: Fri, 06 Feb 2009 17:31:37 -0800
Cc: James Craig <jcraig@apple.com>, public-html@w3.org
Message-id: <CFD91A7C-D8FD-48E1-9D12-B3A51EB0BFF9@apple.com>
To: Ian Hickson <ian@hixie.ch>


On Feb 6, 2009, at 4:10 PM, Ian Hickson wrote:

>
> On Fri, 6 Feb 2009, James Craig wrote:
>>>>
>>>> 6. If no caption information can be determined from the previous
>>>> steps, user agents MAY assume the image is a key part of the  
>>>> content
>>>> lacking a textual equivalent in the document
>>>
>>> What does this require? Could you describe a test page that
>>> demonstrates how to test whether a user agent is complying to this
>>> requirement or not?
>>>
>>> There's no point adding requirements that aren't testable.
>>
>> Do you need to test an RFC 2119 "MAY"?
>
> It has to be testable, otherwise it's meaningless as a requirement.  
> MAY
> requirements (and actually even SHOULD requirements) aren't likely  
> to be
> tested in a conformance test suite, though, no.

I don't think MAY-level requirements need to be testable, because they  
are not really requirements. Rather, they explicitly grant freedom to  
the relevant conformance class.

For example, if you give an explicit algorithm in pseudo-code for some  
calculation, and that pseudo-code is known to be a slow but clear  
algorithm, you could say something like "User agents MAY calculate  
value X using other algorithms, so long as the answer is the same as  
that produced by this algorithm". That can't be tested, but it's not  
an invalid requirement, in my opinion. (Of course, permission to use  
faster but black-box equivalent algorithms generally goes without  
saying, but I can imagine similar cases where a MAY has no directly  
observable effect.)

That being said, I am not sure the specific statement James suggested  
is necessary.

Regards,
Maciej
Received on Saturday, 7 February 2009 01:32:19 UTC

This archive was generated by hypermail 2.3.1 : Monday, 29 September 2014 09:39:01 UTC