@function --bar() {
--x: 42;
@@ -1728,6 +1728,258 @@ The {{CSSFunctionDeclarations}} rule, like {{CSSNestedDeclarations}},
[=serialize a CSS rule|serializes=] as if its [=CSS declaration block|declaration block=]
had been [=serialize a CSS declaration block|serialized=] directly.
+The {{CSSMixinRule}} Interface {#the-mixin-interface}
+-----------------------------------------------------
+
+The {{CSSMixinRule}} interface represents a ''@mixin'' rule.
+
+
+[Exposed=Window]
+interface CSSMixinRule : CSSGroupingRule {
+ readonly attribute CSSOMString name;
+ sequence<FunctionParameter> getParameters();
+ readonly attribute boolean contents;
+};
+
+
+
+ - name
+
-
+ The result of [=serialize an identifier=]
+ on the [=mixin=]'s name.
+
- getParameters()
+
-
+ Returns [=function parameters=] associated with the [=mixin=],
+ excluding any '@contents' parameter.
+
+ - contents
+
-
+ True if the [=mixin=] accepts a [=contents block=],
+ and false otherwise.
+
+
+While declarations may be specified directly within a ''@mixin'' rule,
+they are not represented as such in the CSSOM.
+Instead, consecutive segments of declarations
+appear as if wrapped in {{CSSNestedDeclarations}} rules.
+
+
+
+To
serialize a CSSMixinRule,
+return the concatenation of the following:
+
+ 1. The string
"@mixin" followed by a single SPACE (U+0020).
+ 2. The result of performing
serialize an identifier
+ on the name of the [=mixin=],
+ followed by a single LEFT PARENTHESIS (U+0028).
+ 3. The result of [=serialize a function parameter=]
+ on each of the [=mixin's=] [=function parameter|parameters=],
+ all joined by
", "
+ (COMMA U+002C, followed by a single SPACE U+0020).
+ 4. A single RIGHT PARENTHESIS (U+0029).
+ 5. A single LEFT CURLY BRACKET (U+007B),
+ followed by a SPACE (U+0020).
+ 6. The result of performing [=serialize a CSS rule=]
+ on each rule in cssRules,
+ filtering out empty strings,
+ all joined by a single SPACE (U+0020).
+ 7. A single SPACE (U+0020),
+ followed by a single RIGHT CURLY BRACKET (U+007D).
+
+
+The {{CSSApplyBlockRule}} Interface {#the-apply-block-interface}
+----------------------------------------------------------------
+
+The {{CSSApplyBlockRule}} interface represents
+an ''@apply'' rule with a [=contents block=].
+
+
+[Exposed=Window]
+interface CSSApplyBlockRule : CSSGroupingRule {
+ readonly attribute CSSOMString name;
+ sequence<CSSOMString> getArguments();
+};
+
+
+
+ - name
+
-
+ If the ''@apply'' rule has an associated <>,
+ the result of [=serialize an identifier=] on that [=ident=].
+ Otherwise,
+ the result of [=serialize an identifier=] on the name
+ of the associated <>.
+
+ - getArguments()
+
-
+ Returns a sequence of arguments as strings,
+ each item [[css-variables-1#serializing-custom-props|serialized]]
+ as if it had been the specified value of a [=custom property=].
+
+
+
+The [=CSSRule/child CSS rules=] of a {{CSSApplyBlockRule}}
+represent the [=contents block=]
+of the ''@apply'' rule.
+
+As for {{CSSMixinRule}},
+consecutive segments of declarations
+specified directly within the [=contents block=] of an ''@apply'' rule
+are represented as {{CSSNestedDeclarations}}.
+
+
+To serialize a CSSApplyBlockRule,
+return the concatenation of the following:
+
+ 1. The string "@apply" followed by a single SPACE (U+0020).
+ 2. The result of performing [=serialize an @apply prelude=]
+ on the ''@apply'' rule.
+ 3. A single SPACE (U+0020).
+ 4. A single LEFT CURLY BRACKET (U+007B),
+ followed by a SPACE (U+0020).
+ 5. The result of performing [=serialize a CSS rule=]
+ on each rule in cssRules,
+ filtering out empty strings,
+ all joined by a single SPACE (U+0020).
+ 6. A single SPACE (U+0020),
+ followed by a RIGHT CURLY BRACKET (U+007D).
+
+
+
+To serialize an @apply prelude,
+given an ''@apply'' rule,
+return the concatenation of the following:
+
+ 1. The {{CSSApplyBlockRule/name}} of the ''@apply'' rule.
+ 2. If the ''@apply'' rule has at least one argument,
+ the concatenation of:
+ * A single LEFT PARENTHESIS (U+0028).
+ * The result of performing [=serialize a function argument=]
+ on each argument,
+ all joined by ", ".
+ * A single RIGHT PARENTHESIS (U+0029).
+
+
+
+To
serialize a function argument,
+given a <
> |argument|:
+
+ 1. [[css-variables-1#serializing-custom-props|Serialize]] |argument|
+ as if it had been the specified value of a [=custom property=],
+ and let |serialized argument| be the result.
+
+ This means that an argument serializes exactly as written,
+ except with leading and trailing whitespace removed.
+
+ 2. If |serialized argument| does not contain any top-level <>s,
+ nor any top-level <<{-token>>s,
+ return |serialized argument|.
+ 3. Otherwise, return the concatenation of the following:
+ * A single LEFT CURLY BRACKET (U+007B),
+ followed by a SPACE (U+0020).
+ * The value of |serialized argument|.
+ * A single SPACE (U+0020),
+ followed by a RIGHT CURLY BRACKET (U+007D).
+
+
+ See [[css-values-5#component-function-commas]] for more information
+ on [=comma-containing productions=].
+
+
+
+The {{CSSApplyStatementRule}} Interface {#the-apply-statement-interface}
+------------------------------------------------------------------------
+
+The {{CSSApplyStatementRule}} interface represents
+an ''@apply'' rule without a [=contents block=].
+
+
+[Exposed=Window]
+interface CSSApplyStatementRule : CSSRule {
+ readonly attribute CSSOMString name;
+ sequence<CSSOMString> getArguments();
+};
+
+
+
+ - name
+
-
+ The same as {{CSSApplyBlockRule/name|CSSApplyBlockRule.name}}.
+
+ - getArguments()
+
-
+ The same as {{CSSApplyBlockRule/getArguments()|CSSApplyBlockRule.getArguments()}}.
+
+
+
+
+To serialize a CSSApplyStatementRule,
+return the concatenation of the following:
+
+ 1. The string "@apply" followed by a single SPACE (U+0020).
+ 2. The result of performing [=serialize an @apply prelude=]
+ on the ''@apply'' rule.
+ 3. A single SEMICOLON (U+003B).
+
+
+The {{CSSContentsBlockRule}} Interface {#the-contents-block-interface}
+---------------------------------------------------------------------
+
+The {{CSSContentsBlockRule}} interface represents
+a ''@contents'' rule with a [=fallback block=].
+
+
+[Exposed=Window]
+interface CSSContentsBlockRule : CSSGroupingRule { };
+
+
+The [=CSSRule/child CSS rules=] of a {{CSSContentsBlockRule}}
+represent the [=fallback block=]
+of the ''@contents'' rule.
+
+As for {{CSSMixinRule}} and {{CSSApplyBlockRule}},
+consecutive segments of declarations
+specified directly within the [=fallback block=] of a ''@contents'' rule
+are represented as {{CSSNestedDeclarations}}.
+
+
+To serialize a CSSContentsBlockRule,
+return the concatenation of the following:
+
+ 1. The string "@contents" followed by a single SPACE (U+0020).
+ 2. A single LEFT CURLY BRACKET (U+007B),
+ followed by a SPACE (U+0020).
+ 3. The result of performing [=serialize a CSS rule=]
+ on each rule in cssRules,
+ filtering out empty strings,
+ all joined by a single SPACE (U+0020).
+ 4. A single SPACE (U+0020),
+ followed by a RIGHT CURLY BRACKET (U+007D).
+
+
+The {{CSSContentsStatementRule}} Interface {#the-contents-statement-interface}
+------------------------------------------------------------------------------
+
+The {{CSSContentsStatementRule}} interface represents
+a ''@contents'' rule without a [=fallback block=].
+
+
+[Exposed=Window]
+interface CSSContentsStatementRule : CSSRule { };
+
+
+
+To serialize a CSSContentsStatementRule,
+return the string "@contents",
+followed by a single SEMICOLON (U+003B).
+
+
Privacy Considerations {#privacy}
===============================================
diff --git a/cssom-1/Overview.bs b/cssom-1/Overview.bs
index c0249153e30d..222e25055fd9 100644
--- a/cssom-1/Overview.bs
+++ b/cssom-1/Overview.bs
@@ -1808,7 +1808,7 @@ null.
A reference to a parent CSS style sheet or null.
This item is initialized to reference an associated style sheet when the rule is created. It can be changed to null.
-child CSS rules
+child CSS rules
A list of child CSS rules. The list can be mutated.