[whatwg] Dimension attributes and video

Ian Hickson ian at hixie.ch
Wed Feb 25 15:41:54 PST 2009

On Wed, 25 Feb 2009, Boris Zbarsky wrote:
> I was just trying to figure out what the width and height attributes are
> supposed to do on <video>.  Section 4.8.7 of the spec lists these attributes
> as being possible content attributes, but that list doesn't link to
> definitions of the attributes.

It actually does, but I introduced a bug in the style sheet last night 
that made the links not work. I've fixed this. Sorry about that!

With the links functioning, does it make sense?

> This would all be more readable if there were a section for each 
> attribute involved (or a single section for width+height if that makes 
> more sense) that somehow set off the attribute name and then what it 
> does.

Yeah, I've considered doing that. The problem is that it doesn't always 
really fit with the conforming criteria. Sometimes I have to define an 
attribute two or three times with different requirements based on the 
value of another attribute, for example.

> The DOM specs do a pretty good job of a setup like this.

I've found the setup in the DOM specs leads to the conformance criteria 
being woefully inadequate, because it forces one to think of the 
attributes are independent features, and leaves no room for defining the 
common processing model.

> Past that, the "dimension attributes" section (4.8.17) doesn't tell me, as a
> UA implementor, much about what they do.  It's not even clear whether the
> inequalities given are authoring requirements or implementation ones (though I
> assume the former).

Yes, these are authoring constraints. It's not clear to me what the 
constraints would mean for implementations. I've tried to make it clearer. 
Is that better?

> It's not clear why those requirements are there at all: why shouldn't 
> one stretch "the image" [sic] using these attributes?  That's commonly 
> done for <img>!

The idea is to reduce the use of presentational images in HTML.

> Also, why should the attributes be omitted "if the resource in question 
> does not have both an intrinsic width and an intrinsic height"?

Because purely presentational concerns belong in the styling layer.

> But worst of all, the only mention of what a UA is to do with these 
> attributes is "give the dimensions of the visual content of the element 
> (the width and height respectively, relative to the nominal direction of 
> the output medium), in CSS pixels."  That doesn't tell me much.

I've added a link from that section to the rendering section which 
actually defines what the user agent is expected to do with the 
attributes. I hope that helps.

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

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