Re: clarification on normative and informative

On Tue, 26 Feb 2008, Steven Faulkner wrote:
> 
> I have read the section of the spec in relation to 
> normative/informative, but it is still unlcear to me. Can you clarify 
> what parts of the img section are normative and which are informative:
> 
> for example:
> 
> "A graphical representation of some of the surrounding text
> 
> In many cases, the image is actually just supplementary, and its 
> presence merely reinforces the surrounding text. In these cases, the 
> alt<http://www.w3.org/html/wg/html5/#alt>attribute must be present but 
> its value must be the empty string."
> 
> Is the above normative or informative? or a mixture?

A mixture. This sentence:

   "In many cases, the image is actually just supplementary, and its 
   presence merely reinforces the surrounding text."

...is an informative statement (as it doesn't introduce any requirements). 

This sentence:

   "In these cases, the alt attribute must be present but its value must 
   be the empty string."

...is normative and makes two requirements. It says that in the cases 
referred to by the previous sentence (that is, when the image is actually 
just supplementary, and its presence merely reinforces the surrounding 
text), there are two requirements that documents/authors must obey, namely 
that the relevant <img> elements must have empty alt="" attributes 
specified.


> and this example:
> 
> "The img <http://www.w3.org/html/wg/html5/#img> must not be used as a 
> layout tool. In particular, img <http://www.w3.org/html/wg/html5/#img> 
> elements should not be used to display fully transparent images, as they 
> rarely convey meaning and rarely add anything useful to the document. "

This paragraph has two normative requirements.

The first is an aboslute requirement on documents/authors, requiring that 
they never use <img> elements for layout-specific purposes. "MUST" means 
it's an absolute requirement.

The second says gives a specific case, but relaxes the requirement for 
this specific case to be less absolute, as there may be cases where it 
does not apply. It says that transparent images are not to be used (and 
gives a reason why), but it allows for the cases where transparent images 
might be appropriate for non-layout reasons. For example, a Web page 
might include an image purporting to be a depiction of the invisible pink 
unicorn, which could be a completely transparent image. In that case, it's 
not a layout image, and so we don't want to ban it. "SHOULD" means it's 
not an absolute reuiqmrent, but that there must be a damn good reason for 
the requirement to be ignored.



This blog entry may be of help:

   http://ln.hixie.ch/?start=1140242962&count=1

HTH,
-- 
Ian Hickson               U+1047E                )\._.,--....,'``.    fL
http://ln.hixie.ch/       U+263A                /,   _.. \   _\  ;`._ ,.
Things that are impossible just take longer.   `._.-(,_..'--(,_..'`-.;.'

Received on Tuesday, 26 February 2008 11:33:30 UTC