User Settings Being Overridden by <template> settings

[snuggs]

TL;DR; User attribute settings should take prescedence over template defaults.

This issue effects Attributes defined on a custom element within the master document being overridden by template defaults.

Example

Master Document

<link rel=import href=foo-bar.html>

<foo-bar title='I want my title'></foo-bar>

Imported Document

<template title='This is the template title'></template>

<script>
Element `foo-bar`
  (class extends HTMLElement {})
</script>

Resulting Master Document

<link rel=import href=foo-bar.html>

<foo-bar title='This is the template title'></foo-bar>

Expected Master Document

<foo-bar title='I want my title'></foo-bar>

[brandondees]

we gotta have a test case covering this, it's super fundamentally important to preserve

[snuggs]

Seems like this is going to be difficult @brandondees as there is no support...yet...

Had an issue closed down jsdom/jsdom#1900
And didn't realize already had an issue open. jsdom/jsdom#1030 (comment)
And currently a PR gaining some traction jsdom/jsdom#1872

[brandondees]

the test case is difficult, or the implementation? if JSDOM doesn't implement specs that's not our problem, we can test on headless chrome or whatever else.

[snuggs]

You've got a point @brandondees ... 🤔

[snuggs]

Fixed.