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Re: [css-writing-modes][svg] Embedded SVG and inheritance

From: Koji Ishii <kojiishi@gmail.com>
Date: Sun, 10 May 2015 21:17:26 +0900
Message-ID: <CAN9ydbVzaorAfrbfD6voPE32Prb55+NwxWhBU0Bhzk-DUxXTMw@mail.gmail.com>
To: Leonard Rosenthol <lrosenth@adobe.com>
Cc: "Tab Atkins Jr." <jackalmage@gmail.com>, fantasai <fantasai.lists@inkedblade.net>, Jonathan Kew <jfkthame@gmail.com>, "www-style@w3.org" <www-style@w3.org>, SVG WG <w3c-svg-wg@w3.org>, Brady Duga <duga@google.com>, www-svg <www-svg@w3.org>
After learned a bit of SVG, I understand this issue is more
complicated than thought.

Amelia and Leonard suggested that SVG wants to inherit when SVG is
used to style text within HTML (e.g., decorative headings) cases.
fantasai and I had a mind that SVG when used as an image should not
inherit. I understand these are two separate use cases and desired
behavior vary.

So the discussions we need are:
1. How to allow authors to switch between these two models
2. Which is default -- opt-in or opt-out

My guess is that use-as-image is more common, and I prefer to default
to it, but I don't have any data on it.

Tab suggested that moving to opt-in by default can break the web compat.

The current situation is more complex than I thought.

The color property, for instance, inherits, but it does not affect
unless author specifically use, for instance, fill="currentColor".
Without the fill attribute set to "currentColor", <text> renders in
black, not the value of the color property, so it's an "opt-in" model
to inherit.

The font-variant inherits and has the same syntax on the same
property, so it's an "opt-out" model to inherit. But practically it's
unlikely to apply font-variant to whole document.

The writing-mode has additional complexity here:
a. Blink/WebKit is opt-in today because of prefix and renaming. IE is
opt-out, Gecko Nightly is opt-out (but hasn't shipped yet)
b. Even if we inherit, it'll simply break the SVG document, because
SVG uses physical coordinates. Changing writing-mode without changing
coordinate and spacing system will simply result in broken pictures.
c. Spec-wise, how to interpret "vertical-rl" value in SVG when
inherited is undefined, which I suppose to mean invalid. Implementing
this behavior does not make much sense to me, so I wish the spec to
change. Gecko already handles this according to Jonathan.
d. Spec-wise, how to interpret "tb-rl" value in HTML is "wish to".
Should we change this to "should" for better interoperability?

So for writing-mode, regardless of #1/#2 above, I think we should define:
3. writing-mode should not inherit into SVG.
4. Consider Tab's nested cases more in depth, and come up with
necessary actions.
5. Clarify how to interpret renamed values better, in HTML and SVG.

Thoughts?

/koji
Received on Sunday, 10 May 2015 12:17:53 UTC

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