Also no browser vendors that flat out refuse to implement parts of the spec (Apple [0]), or block proposals unless implemented in a highly specific way (all, here's one example [1], ugh politics).
[0] https://bugs.webkit.org/show_bug.cgi?id=182671
[1] https://github.com/WICG/webcomponents/issues/587#issuecommen...
<template tag="test"><h1>works</h1></template> <test/>
But it's the same rationale IIRC why built-in components are not extensible (even if this was one of the original promises): the browser has no way of knowing about the actual behavior of the object, which leads to all kinds of mess inside the engine.
The validity of Apple's reasoning makes it even stranger.
Quite recently Constructible Stylesheets were released in Chrome:
- because lit wanted them
- despite Firefox and Safari being against the state of the spec
- despite Safari clearly stating they are not going to implement the spec, ever (there was a trivially reproducible race condition in the spec)
The entire discussion here: https://github.com/WICG/construct-stylesheets/issues/45#issu...