[css-masking] Change initial value of mask-repeat and mask-position

[SebastianZ]

As of w3c/csswg-drafts#599 mask-repeat should have repeat and mask-position should have 0% 0% as initial value according to the initial values in WebKit/Blink.

@tabatkins mentioned that there was a resolution on this, though unfortunately I couldn't find the related minutes.

Gecko also changed those values lately to the ones mentioned above.

Sebastian

[csnardi]

It looks like the minutes for this are in https://lists.w3.org/Archives/Public/www-style/2016Oct/0130.html:

<Rossen> https://github.com/w3c/csswg-drafts/issues/599
 dbaron: At some point we resolved that mask-repeat and
         mask-position have different initial values than
         background. It's not compat with webkit-mask-repeat and
         webkit-mask-position. There's a bunch of web content that
         depends on the values. We've had what the spec says in FF.
 dbaron: We've gotten some of the sites to fix the behavior. We do
         still have compat problems.
 dbaron: Question is; we're close to rolling back and doing same
         initial values as background-position.
 dbaron: In the chromium bug there was a suggestion that we behave
         different for prefix and unprefix though it's not clear to
         me how you do that. If everyone uses shorthand maybe
         webkit-mask shorthand would specify different values. I
         don't have data on shorthand usage.
 dbaron: We're having enough compat problems we're likely to roll
         back.
 Rossen: Any other opinions?

 TabAtkins: We're for keeping spec as-is. Though twitter fixed it
            there's likely other stuff around. no-repeat is a
            better value in isolation in mask, masking for similar
            properties makes sense too. I'm fine changing spec to
            match Chrome behavior.
 Rossen: Any objections to matching webkit/blink behavior and
         record that into the spec?
 fantasai: Do we have a editor?
 TabAtkins: Kinda? krit is technically the editor but shane and I
            will do edits.
 fantasai: There were some other issues with masking that I'm
           guessing isn't edited in. They may be on stats page. We
           need an active editor for masking.
 <ChrisL> agree we need an active editor for masking
 Rossen: That's a great point.

 RESOLVED: match webkit/blink behavior

 Rossen: Next we need official editors. I heard TabAtkins and shane
        stepping in. Yes?
 TabAtkins: Yep.
 <krit> I would welcome another active editor on mask
 Rossen: Anyone else want to be an editor?
 ChrisL: TabAtkins you edit an awful lot of specs.
 ChrisL: Applying TabAtkins doesn't necessarily increase output.
 TabAtkins: Which is why we're adding shane as well.
 ChrisL: This is graphics-y. I'd be interested.
 Rossen: Okay, so ChrisL TabAtkins and shane as editors for masking
         spec?

 RESOLVED: ChrisL, TabAtkins, and shane as editors for masking spec.

 Rossen: That means you guys get to do all the actions and
         resolutions retroactively.