[css-scoping-2] Create initial diff-spec for scope level 2

Author: mirisuzanne

css-scoping-2/Overview.bs

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+<pre class='metadata'>
+Title: CSS Scoping Module Level 2
+Level: 2
+Shortname: css-scoping
+Group: CSSWG
+Status: ED
+Work Status: Exploring
+TR: https://www.w3.org/TR/css-scoping-1/
+ED: https://drafts.csswg.org/css-scoping/
+Editor: Tab Atkins Jr., Google, http://xanthir.com/contact/, w3cid 42199
+Editor: Miriam E. Suzanne, Invited Expert, http://miriamsuzanne.com/contact, w3cid 117151
+Abstract: This specification defines scoping/encapsulation mechanisms for CSS.
+Ignored Terms: inherit, slot, custom elements, stylesheets
+Ignored Vars: root elements
+</pre>
+
+<pre class="link-defaults">
+spec:dom; type:dfn;
+	text:host
+	text:shadow root; for:/
+	text:root; for:tree
+	text:find slottables
+	text:find flattened slottables
+	text:element; for:/
+spec:html; type:element; text:style
+spec:selectors-4; type:dfn;
+	text: static profile
+	text: dynamic profile
+spec:css-pseudo-4; type:selector;
+	text:::before
+	text:::after
+spec:cascade-4; type:dfn; text: inherit
+</pre>
+
+<h2 id="intro">
+Introduction</h2>
+
+	Issue: This is a diff spec over <a href="https://www.w3.org/TR/css-scoping-1/">CSS Scoping Module Level 1</a>.
+	It is currently an Exploratory Working Draft:
+	if you are implementing anything, please use Level 1 as a reference.
+	We will merge the Level 1 text into this draft once it reaches CR.
+
+
+<!--
+████████  ████████ ████████    ███    ██     ██ ██       ████████
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+-->
+
+<h2 id='default-element-styles'>
+Default Styles for Custom Elements</h2>
+
+	Issue: [[css-scoping-1#default-element-styles]]
+
+<!--
+ ██████  ██     ██    ███    ████████   ███████  ██      ██
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+ ██████  ██     ██ ██     ██ ████████   ███████   ███  ███
+-->
+
+<h2 id='shadow-dom'>
+Shadow Encapsulation</h2>
+
+	Issue: [[css-scoping-1#shadow-dom]]
+
+<!--
+ ██████   ██████   ███████  ████████  ████ ██    ██  ██████
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+-->
+
+<h2 id='scope'>
+Scoped Styles</h2>
+
+	Issue: Introduce scoped styles
+
+<!--
+ ███████   ██████   ██████   ███████  ████████  ████████
+██     ██ ██    ██ ██    ██ ██     ██ ██     ██ ██
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+ ███████   ██████   ██████   ███████  ██        ████████
+-->
+
+<h3 id='scope-atrule'>
+Scoping Styles in CSS: the ''@scope'' rule</h3>
+
+	The <dfn>@scope</dfn> at-rule allows authors to create scoped style rules using CSS syntax.
+	The syntax of the ''@scope'' rule is:
+
+	<pre class='prod'>
+	@scope (<<selector-list>>) [to (<<selector-list>>)]? {
+		<<stylesheet>>
+	}
+	</pre>
+
+	Issue: Define the ''@scope'' rule
+	Issue: Define scope proximity in the cascade (cross-reference css-cascade)
+
+<h3 id='in-scope-selector'>
+Selecting inside a scope: the '':in-scope'' pseudo-class</h3>
+
+	The <dfn>:in-scope</dfn> pseudo-class allows authors to
+	select elements that are within a given scope.
+
+	Issue: Define an '':in-scope'' selector (cross-reference css-selectors)
+
+<h2 id="changes">
+Changes</h2>
+
+<h3 id="additions-l">
+Additions Since Level 1</h3>
+
+	The following features have been added since
+	<a href="https://www.w3.org/TR/css-scoping-1/">Level 1</a>:
+
+	* The ''@scope'' rule
+	* The '':in-scope()'' pseudo-class
+
+Privacy and Security Considerations {#priv-sec}
+===============================================
+
+This specification introduces Shadow DOM and some shadow-piercing capabilities,
+but this does not introduce any privacy or security issues--
+shadow DOM, as currently specified, is intentionally not a privacy/security boundary
+(and the parts of the UA that use shadow DOM and <em>do</em> have a privacy/security boundary
+implicitly rely on protections not yet specified,
+which protect them from the things defined in this specification).
+