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[css3-background] comments

From: Anne van Kesteren <fora@annevankesteren.nl>
Date: Sat, 09 Apr 2005 14:08:09 +0200
Message-ID: <4257C5A9.5060005@annevankesteren.nl>
To: W3C CSS List <www-style@w3.org>

I think the specification should have a section that clarifies the terms
SHOULD, MUST, etc. The rest of the comments I gave per section. I might 
have missed a few bits, I'll reread the draft when it becomes last call.

* 1. Dependencies with other CSS 3 Modules

Does it really depend on those modules? I think this section need to be
revised. Probably on all CSS3 modules as the graph that was produced a
few weeks ago doesn't seem to be correct. A specification that
implements the CSS3 Background module does not need the 'rgba' color
value for example. It would be nice, but it doesn't depend on it.

* 2.1. Changes from CSS 2.1

There are new 'border' properties as well. 'box-shadow' wasn't in CSS
2.1 either.

* 5. The 'background-image' property

# An image that is empty (zero width or zero height), that fails to
# download, or that otherwise cannot be displayed (e.g., because it is
# not in a supported image format) has the same effect as a non-empty
# transparent image.

Wouldn't it be easier to specify that if an image can't be displayed the
initial value should be used instead?

# If 'background-repeat' or 'background-position' has more
# comma-separated values than 'background-image', the series of values
# is repeated as needed.

As the editor's note already mentioned, it makes more sense for
'background-image' to determine the number of layer and let all the
extra values specified be ignored.

Actually, it might make even more sense to fall back to the initial
value when one of the properties specifies a layer too much. For
'background-image' that would be 'none' if either 'background-repeat' or
'background-position' has more comma-separated values.

# Editor's Note: Conformance properties for an image should be
# addressed here: MIME type image/*, require support for PNG, refer to
# profiles…

I don't think it is up to the CSS WG to require support for images.

* 6. The 'background-repeat' property

# Should there also be values of "repeat-up", "repeat-down",
# "repeat-right", and "repeat-left" for this property?

What exactly would these values do?

I think it might be wise to specify how 'space' should work. I am aware
of a large discussion how 'letter-spacing' should be implemented exactly
and it would  be nice if this module would specify in more detail how it
should work. (Personally I think the space at the edge should be halve
the space that is between the images.)

* 8. The 'background-position' property

It would be nice to have a way to position a background from somewhere
else than '0 0' (top left). Using the 'calc()' proposal to express what
I mean:

  background-position:calc(100%-5px) calc(100%-5px);

... it would be very nice if that was made possible. Perhaps using '-5px
-5px' or so.

Or, to determinate the canvas in which the 'background-image' is drawn. 
Such a possibility would also remove the need for the editor's note in 
section 9 and probably remove the need for section 10.

* 11. The 'background-size' property

I'm not sure if this is useful at all. I don't see that a stretched -- 
it is a better name, indeed -- image could work out nice and I expect 
authors to not take advantages of the possiblities. This also introduces 
complexity for UAs and all kinds of rounding issues/errors. I suggest 
marking this as a feature at risk if it is desired by the WG to keep it.

* 16. The 'border-style' properties

I think this should specify that UAs are allowed to fallback to 'solid' 
if they don't have an appropriate implementation for the specified 
values. I think this might be useful for UAs implementating 'border-radius'.

* 18. The 'border-image' property

Again, this makes me wonder how UAs are going to do this "correctly". 
The idea is quite nice, although it seems strange that a 'border' 
property sets the background image...

* 23. The background of the canvas

I think the specification should not give any recommendations anymore to 
authors. Most UAs have implemented support for 'background' on the root 
element. (Even Internet Explorer, be it just for 'background-color'.) I 
also think it should say XHTML/XML or just XML.

* 26. Tests

How can a basic test suite guarentee interoparable implementations? Test 
suites have to be detailed. I'd argue tests are more important than the 

  Anne van Kesteren
Received on Saturday, 9 April 2005 12:07:55 UTC

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