[css-transforms-2] Explicitly specify that a transform is a containing block for all descendants

[smfr]

https://www.w3.org/Bugs/Public/show_bug.cgi?id=16328

Comment: https://www.w3.org/Bugs/Public/show_bug.cgi?id=16328
Comment: http://www.w3.org/mid/514E058C.5060105@exyr.org

Also
Comment: https://www.w3.org/mid/24BE3FE7-60C9-4690-A01C-F2291460DE7F@adobe.com
Comment: https://www.w3.org/mid/20151125002414.GA22745@pescadero.dbaron.org

[mikemcguire]

WOAH! moving issues to github, +1 for that and +1 for resolving this issue

[tomasdev]

Are there any plans on fixing this?

http://jsbin.com/jazuwus/edit?html,css,output

[asiljan]

+1

[chrishtr]

Is this issue removing transform as a containing block for fixed-position elements? I don't think
that is a good idea, as it:

• makes clipping and filter effects hard to define and implement, and in general ill-defined because
  it's impossible to "filter" across multiple 2d planes.
• introduces difficult and complex code to implement compositing
• makes it hard to provide clean fast paths for transforms

[mikemcguire]

Im not going to pretend to understand the difficulties in implementing the client code cause I'm completely unqualified. But want to put my two cents in. When I ran into this issue I sat stumped forever. While this issue is now well documented on the web, it took me forever to actually figure out that the transform is what was causing the issue and thus being able to find the chrome bug filed and eventually the original Bugzilla spec bug to request an update.

It seems counter-intuitive to not update the spec with what seems to be a universal expectation to accommodate the Chrome team. Especially since other browsers are accommodating what seems to be universally expected.

Additionally, while the spec for positioned elements outlines this issue, I find it difficult to understand the language used in the spec. Front-end devs could potentially waste a lot of time looking for a fix, and possibly explains a lack of interest for this issue. I personally find that the transforms spec more clearly outlines the behavior than the positioning spec.

[RByers]

I believe #1945 tracks doing exactly that - updating the spec to match Chrome's behavior. Merged.

[RByers]

I verified that Firefox, Edge (14 and 16), Chrome and Safari all behave the same here. Only IE appears not to create a containing block for a transform. So definitely we just need to update the spec and web-platform-tests for this.

For the record, here's the relevant chromium issue.