Do we need a rendering spec?

Hello public-webapps,

As HTML imports [1] are implemented across browsers, there’s a potential
for diversity of opinion in how rendering of documents with imports occurs.
What blocks rendering? What doesn’t? To prevent the inevitable pain of
converging on a de-facto standard behavior, it would be super-nice to have
precise documentation of when the rendering engine should start (and stop)
rendering the document.

The specific problem we (the imports people) are interested in is “when do
things first appear on screen?”, and we could definitely hack up some vague
informative prose in the HTML Imports spec in the short term.

But long-term, do we (the W3C people) want a rendering spec?

It seems like a daunting path with lots of obstacles. To name a few:

* Things like first-frame rendering traditionally had been a secret sauce
for performance optimizations. Trying to standardize this could potentially
remove such opportunities.

* Rendering as a concept doesn’t seem to exist in spec land. Starting from
scratch will be a ton of work.

* Browsers do wildly different things when rendering. Coming up with a
cohesive unified spec for existing behaviors sounds like an epic multi-year
undertaking.

* Even more fundamentally, what is really rendering? Is it when the pixels
appear on screen? Is it the specific consistent state of the box tree?
Hell, do we have to now define a box tree?

What do you folks think? Ideas/feedback/insights are appreciated.

[1] http://w3c.github.io/webcomponents/spec/imports/

:DG<