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[css3-values][css3-page] Viewport-percentage length units in the page context.

From: Simon Sapin <simon.sapin@kozea.fr>
Date: Sat, 13 Oct 2012 10:55:17 +0200
Message-ID: <50792C75.80100@kozea.fr>
To: WWW Style <www-style@w3.org>

css3-values defines the vw, vh, vmin and vmax units relative to the 
initial containing block.

In css3-page, this ICB is the content area of the page box which is 
itself based on some of the pageís properties. [1]

Now, what do the new viewport-percentage units means for these 
properties in the page context? Itís easy to construct a circular 
dependency like:

     @page { width: 200vw }

Ö or dozens of other combinations. We need to break the cycle at some 
point to get a well-defined behavior. I suggest making the 
viewport-percentage units invalid (as they were before css3-values) in 
the page context, either:

* On the problematic properties only [1], or
* On all properties in the page context, for simplicity and consistency

[1] 'size', 'width', 'height', 'margin-*', 'border-*-width', 'padding-*' 
and, through em or ex values, 'font-size'. Am I missing any?

While writing this, I notice another kind of cycle. css3-page defines: 
"The page context inherits from the root element." How about this?

     :root { font-size: 1vw }
     @page { width: 200em }

I canít find a satisfying way to resolve this one. Any ideas?

Simon Sapin
Received on Saturday, 13 October 2012 08:56:05 UTC

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