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Re: template namespace attribute proposal

From: Benjamin Lesh <blesh@netflix.com>
Date: Mon, 16 Mar 2015 10:45:58 -0700
Message-ID: <CADcN1GBVXWPz_FLoW5erO4xgb8WfZA=_ykJjY3iHrfjB0RJLdg@mail.gmail.com>
To: Austin William Wright <aaa@bzfx.net>
Cc: Anne van Kesteren <annevk@annevk.nl>, Adam Klein <adamk@chromium.org>, WebApps WG <public-webapps@w3.org>
> Could you post the specific regression you ran into?

Specifically this was around platform development. Let's say I have my
developers (those that use my platform) all define their templates in
<template/> tags. This is used for all components, including components
that are partials or are "composable"... One specific example is this:

<my-graph domainx="0,100" width="200" domainy="0,100" height="100">
  <my-line data="0,1 1,1 2,2 3,3 4,4 ... snip ... 100, 100"></my-line>

- the shadow root of `<my-graph>` has an <svg> element that contains it's
"content" (which also doesn't work well in SVG).
- the shadow root of `<my-line>` has a <path> element.

So we'd *hope* that you could define the templates for the above (roughly)
as follows:

<template id="my-graph">

<template id="my-line">
  <path />

This, of course, is broken all over the place.

1. Last I checked (6 months ago), <content/> is an SVGElement, not an
2. template#my-line has a `content` with a single HTMLUnknownElement,
meaning trying to use it purely as a document fragment is broken.
3. As the platform author, there is no way for me to know that the
developer intends template#my-line to be an SVG fragment so I can at least
polyfill a solution for them automatically

As a platform author, a namespace attribute would enable me to easily
identify the developer's intent so I can polyfill the behavior before the
browser even supports it.

The idea of having <template> "just work" with SVG without some sort of
attribute like this seems like pie in the sky, and worse, it doesn't give
me an immediate way to solve the problem other than checking the
firstElementChild.tagName of every template and praying developers know the
edge cases like <a/>. Even if it's implemented in every browser, the
developer would still need to know the edge cases. With an attribute, the
developer just needs to know that they're dealing with SVG or not.

On Sat, Mar 14, 2015 at 6:04 PM, Austin William Wright <aaa@bzfx.net> wrote:

> On Thu, Mar 12, 2015 at 4:20 PM, Benjamin Lesh <blesh@netflix.com> wrote:
>> For my part, I disagree slightly with this statement. If you just drop a
>> <circle> tag in a <div>, you're going to get an HTMLUnknownElement. This is
>> by design and to spec, of course. But it unfortunately means you can't
>> clone() the element over to an SVG parent and hope it will work.d
> Could you post the specific regression you ran into? The behavior you
> describe should only true for text/html parsing; it doesn't apply to DOM
> and application/xhtml+xml.
> For instance, given an arbitrary, conforming HTML document containing an
> SVG circle element, this should work:
> var svgns = 'http://www.w3.org/2000/svg';
> var c = document.getElementsByTagNameNS(svgns, 'circle')[0].cloneNode();
> document.getElementsByTagName('body')[0].appendChild(c);
> document.getElementsByTagName('body')[0].lastElementChild.namespaceURI ==
> svgns; // true
> text/html just isn't cut out for the sort of complex stuff we're
> discussing. For instance, what if I want to start using the proposed
> application/api-problem+xml format? You can't. text/html simply isn't built
> for the complex features being proposed. This is made explicit in HTML5:
> The DOM, the HTML syntax, and the XHTML syntax cannot all represent the
> same content. For example, namespaces cannot be represented using the HTML
> syntax, but they are supported in the DOM and in the XHTML syntax.
> Similarly, documents that use the noscript feature can be represented using
> the HTML syntax, but cannot be represented with the DOM or in the XHTML
> syntax. Comments that contain the string "-->" can only be represented in
> the DOM, not in the HTML and XHTML syntaxes.
> There's a craptonne of XML based markup languages and file formats out
> there. We can't just keep importing all of them into HTML every time we
> decide one of them might be useful to embed inside HTML. THERE is a
> usability and complexity nightmare.
> Explicit is better than implicit, so I like the idea of a namespace
> attribute element, it is forward-compatible with future vocabularies we may
> wish to use.
> Namespaces aren't *that* hard to understand. In my code above, I added one
> line declaring the namespace (`var svgns`). Is that really so hard? If you
> want to use the more advanced features of HTML, use namespaces, or import
> whatever vocabulary I want - DocBook, OpenDocument, music notation, XSL,
> without worry of collision. That's what they're there for, and at least a
> handful of client-side libraries already do this, e.g. <http://webodf.org/
> >.
> (Certainly much simpler than, say, the parsing differences between script,
> style, pre, and attributes, which I only understand well enough to know to
> stay the cuss away from putting user content in script tags. The amount of
> inconsistency and complexity of text/html parsing is single-handedly
> responsible for most of the XSS injections I come across. This isn't just
> matter of having a feature or not, this is a matter of security... why not
> fix *this*? /rant)
> I understand the URI may be too much for people to grok, maybe instead use
> a tag name ("html", "svg" or "mathml"):
> <template namespace="svg">
>   <circle cx="10" cy="10" cr="10" />
> </template>
> The application/xhtml+xml parser would simply ignore the namespace
> attribute, using xmlns on children instead. Polyglot HTML would use both
> attributes.
> If two separate attributes is too much, then just add xmlns= support to
> text/html.
> Austin.
Received on Monday, 16 March 2015 17:46:37 UTC

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