Re: [compositing] background-blend-mode on the root element

On 25/06/2014 11:53 PM, Alan Gresley wrote:
> On 21/06/2014 2:42 AM, Rik Cabanier wrote:
>> On Thu, Jun 19, 2014 at 11:29 PM, Alan Gresley <alan@css-class.com>
>> wrote:
>>
>>> On 20/06/2014 12:40 PM, Rik Cabanier wrote:

[snip]

>>>> All browsers implement painting of the root backdrop by drawing the
>>>> background color and images on top of a 100% opaque white backdrop.
>>>>
>>>
>>> This is not quite true. In the Firefox setting for 'Content >
>>> Colors', IE
>>> setting 'Appearance > Colors' and Opera setting for 'Preferences >
>>> Webpages', I can change the background/backdrop of the root element
>>> to at
>>> least a minimum of 70 colors. Internally, each UA has a hidden element
>>> wrapping the root element. For old Opera (not sure about Blink), this
>>> was a
>>> black backdrop.
>>
>>
>> This is unspecified behavior.

Below is the specified behavior. It's what puts the *C* (cascading) into 
CSS.

http://www.w3.org/TR/CSS21/conform.html#style-sheet

   | Style sheets may have three different origins:
   | author, user, and user agent. The interaction
   | of these sources is described in the section
   | on cascading and inheritance.


If we follow the link for cascading and inheritance, we can find a note 
below section 6.4.

http://www.w3.org/TR/CSS21/cascade.html#cascade

   | Note that the user may modify system settings
   | (e.g., system colors) that affect the default
   | style sheet. However, some user agent
   | implementations make it impossible to change
   | the values in the default style sheet.

The last part of section 6.4.1 has the following (this part of the spec 
is not followed by Chrome):

   | Apart from the "!important" setting on
   | individual declarations, this strategy gives
   | author's style sheets higher weight than those
   | of the reader. User agents must give the user
   | the ability to turn off the influence of
   | specific author style sheets, e.g., through
   | a pull-down menu. Conformance to UAAG 1.0
   | checkpoint 4.14 satisfies this condition [UAAG10].

If we follow the link for UAAG10, we arrive at the spec for 'User Agent 
Accessibility Guidelines 1.0' and checkpoint 4.14 is found here.

http://www.w3.org/TR/2002/REC-UAAG10-20021217/guidelines.html#gl-user-control-styles


-- 
Alan Gresley
http://css-3d.org/
http://css-class.com/