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 <>
>> wrote:
>>> On 20/06/2014 12:40 PM, Rik Cabanier wrote:


>>>> 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 

   | 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.

   | 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.

Alan Gresley

Received on Wednesday, 25 June 2014 14:32:05 UTC