diff --git a/CHANGELOG.md b/CHANGELOG.md
index 6dfef18ca..10d6eb63a 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -1,3 +1,12 @@
+## 1.29.0
+
+* Support a broader syntax for `@supports` conditions, based on the latest
+  [Editor's Draft of CSS Conditional Rules 3]. Almost all syntax will be allowed
+  (with interpolation) in the conditions' parentheses, as well as function
+  syntax such as `@supports selector(...)`.
+
+[Editor's Draft of CSS Conditional Rules 3]: https://drafts.csswg.org/css-conditional-3/#at-supports
+
 ## 1.28.0
 
 * Add a [`color.hwb()`] function to `sass:color` that can express colors in [HWB] format.
diff --git a/lib/src/ast/sass.dart b/lib/src/ast/sass.dart
index 93f373b4e..e463a5da7 100644
--- a/lib/src/ast/sass.dart
+++ b/lib/src/ast/sass.dart
@@ -60,7 +60,9 @@ export 'sass/statement/variable_declaration.dart';
 export 'sass/statement/warn_rule.dart';
 export 'sass/statement/while_rule.dart';
 export 'sass/supports_condition.dart';
+export 'sass/supports_condition/anything.dart';
 export 'sass/supports_condition/declaration.dart';
+export 'sass/supports_condition/function.dart';
 export 'sass/supports_condition/interpolation.dart';
 export 'sass/supports_condition/negation.dart';
 export 'sass/supports_condition/operation.dart';
diff --git a/lib/src/ast/sass/supports_condition/anything.dart b/lib/src/ast/sass/supports_condition/anything.dart
new file mode 100644
index 000000000..11e7a4752
--- /dev/null
+++ b/lib/src/ast/sass/supports_condition/anything.dart
@@ -0,0 +1,21 @@
+// Copyright 2020 Google Inc. Use of this source code is governed by an
+// MIT-style license that can be found in the LICENSE file or at
+// https://opensource.org/licenses/MIT.
+
+import 'package:source_span/source_span.dart';
+
+import '../interpolation.dart';
+import '../supports_condition.dart';
+
+/// A supports condition that represents the forwards-compatible
+/// `<general-enclosed>` production.
+class SupportsAnything implements SupportsCondition {
+  /// The contents of the condition.
+  final Interpolation contents;
+
+  final FileSpan span;
+
+  SupportsAnything(this.contents, this.span);
+
+  String toString() => "($contents)";
+}
diff --git a/lib/src/ast/sass/supports_condition/function.dart b/lib/src/ast/sass/supports_condition/function.dart
new file mode 100644
index 000000000..0ca118108
--- /dev/null
+++ b/lib/src/ast/sass/supports_condition/function.dart
@@ -0,0 +1,23 @@
+// Copyright 2020 Google Inc. Use of this source code is governed by an
+// MIT-style license that can be found in the LICENSE file or at
+// https://opensource.org/licenses/MIT.
+
+import 'package:source_span/source_span.dart';
+
+import '../interpolation.dart';
+import '../supports_condition.dart';
+
+/// A function-syntax condition.
+class SupportsFunction implements SupportsCondition {
+  /// The name of the function.
+  final Interpolation name;
+
+  /// The arguments to the function.
+  final Interpolation arguments;
+
+  final FileSpan span;
+
+  SupportsFunction(this.name, this.arguments, this.span);
+
+  String toString() => "$name($arguments)";
+}
diff --git a/lib/src/parse/stylesheet.dart b/lib/src/parse/stylesheet.dart
index 2d609626b..f1739c21f 100644
--- a/lib/src/parse/stylesheet.dart
+++ b/lib/src/parse/stylesheet.dart
@@ -372,7 +372,7 @@ abstract class StylesheetParser extends Parser {
     // Parse custom properties as declarations no matter what.
     var name = nameBuffer.interpolation(scanner.spanFrom(start, beforeColon));
     if (name.initialPlain.startsWith('--')) {
-      var value = _interpolatedDeclarationValue();
+      var value = StringExpression(_interpolatedDeclarationValue());
       expectStatementSeparator("custom property");
       return Declaration(name, scanner.spanFrom(start), value: value);
     }
@@ -538,7 +538,7 @@ abstract class StylesheetParser extends Parser {
     scanner.expectChar($colon);
 
     if (parseCustomProperties && name.initialPlain.startsWith('--')) {
-      var value = _interpolatedDeclarationValue();
+      var value = StringExpression(_interpolatedDeclarationValue());
       expectStatementSeparator("custom property");
       return Declaration(name, scanner.spanFrom(start), value: value);
     }
@@ -2681,8 +2681,7 @@ relase. For details, see http://bit.ly/moz-document.
         return null;
     }
 
-    buffer
-        .addInterpolation(_interpolatedDeclarationValue(allowEmpty: true).text);
+    buffer.addInterpolation(_interpolatedDeclarationValue(allowEmpty: true));
     scanner.expectChar($rparen);
     buffer.writeCharCode($rparen);
 
@@ -2808,8 +2807,7 @@ relase. For details, see http://bit.ly/moz-document.
     buffer
       ..write(name)
       ..writeCharCode($lparen)
-      ..addInterpolation(
-          _interpolatedDeclarationValue(allowEmpty: true).asInterpolation())
+      ..addInterpolation(_interpolatedDeclarationValue(allowEmpty: true))
       ..writeCharCode($rparen);
     if (!scanner.scanChar($rparen)) return false;
     return true;
@@ -2984,10 +2982,18 @@ relase. For details, see http://bit.ly/moz-document.
   ///
   /// If [allowEmpty] is `false` (the default), this requires at least one token.
   ///
+  /// If [allowSemicolon] is `true`, this doesn't stop at semicolons and instead
+  /// includes them in the interpolated output.
+  ///
+  /// If [allowColon] is `false`, this stops at top-level colons.
+  ///
   /// Unlike [declarationValue], this allows interpolation.
-  StringExpression _interpolatedDeclarationValue({bool allowEmpty = false}) {
-    // NOTE: this logic is largely duplicated in Parser.declarationValue and
-    // isIdentifier in utils.dart. Most changes here should be mirrored there.
+  Interpolation _interpolatedDeclarationValue(
+      {bool allowEmpty = false,
+      bool allowSemicolon = false,
+      bool allowColon = true}) {
+    // NOTE: this logic is largely duplicated in Parser.declarationValue. Most
+    // changes here should be mirrored there.
 
     var start = scanner.state;
     var buffer = InterpolationBuffer();
@@ -3065,8 +3071,15 @@ relase. For details, see http://bit.ly/moz-document.
           break;
 
         case $semicolon:
-          if (brackets.isEmpty) break loop;
+          if (!allowSemicolon && brackets.isEmpty) break loop;
+          buffer.writeCharCode(scanner.readChar());
+          wroteNewline = false;
+          break;
+
+        case $colon:
+          if (!allowColon && brackets.isEmpty) break loop;
           buffer.writeCharCode(scanner.readChar());
+          wroteNewline = false;
           break;
 
         case $u:
@@ -3103,7 +3116,7 @@ relase. For details, see http://bit.ly/moz-document.
 
     if (brackets.isNotEmpty) scanner.expectChar(brackets.last);
     if (!allowEmpty && buffer.isEmpty) scanner.error("Expected token.");
-    return StringExpression(buffer.interpolation(scanner.spanFrom(start)));
+    return buffer.interpolation(scanner.spanFrom(start));
   }
 
   /// Consumes an identifier that may contain interpolation.
@@ -3301,10 +3314,7 @@ relase. For details, see http://bit.ly/moz-document.
   /// Consumes a `@supports` condition.
   SupportsCondition _supportsCondition() {
     var start = scanner.state;
-    var first = scanner.peekChar();
-    if (first != $lparen && first != $hash) {
-      var start = scanner.state;
-      expectIdentifier("not");
+    if (scanIdentifier("not")) {
       whitespace();
       return SupportsNegation(
           _supportsConditionInParens(), scanner.spanFrom(start));
@@ -3312,9 +3322,11 @@ relase. For details, see http://bit.ly/moz-document.
 
     var condition = _supportsConditionInParens();
     whitespace();
+    String operator;
     while (lookingAtIdentifier()) {
-      String operator;
-      if (scanIdentifier("or")) {
+      if (operator != null) {
+        expectIdentifier(operator);
+      } else if (scanIdentifier("or")) {
         operator = "or";
       } else {
         expectIdentifier("and");
@@ -3333,56 +3345,126 @@ relase. For details, see http://bit.ly/moz-document.
   /// Consumes a parenthesized supports condition, or an interpolation.
   SupportsCondition _supportsConditionInParens() {
     var start = scanner.state;
-    if (scanner.peekChar() == $hash) {
-      return SupportsInterpolation(
-          singleInterpolation(), scanner.spanFrom(start));
+
+    if (_lookingAtInterpolatedIdentifier()) {
+      var identifier = interpolatedIdentifier();
+      if (identifier.asPlain?.toLowerCase() == "not") {
+        error('"not" is not a valid identifier here.', identifier.span);
+      }
+
+      if (scanner.scanChar($lparen)) {
+        var arguments = _interpolatedDeclarationValue(
+            allowEmpty: true, allowSemicolon: true);
+        scanner.expectChar($rparen);
+        return SupportsFunction(identifier, arguments, scanner.spanFrom(start));
+      } else if (identifier.contents.length != 1 ||
+          identifier.contents.first is! Expression) {
+        error("Expected @supports condition.", identifier.span);
+      } else {
+        return SupportsInterpolation(
+            identifier.contents.first as Expression, scanner.spanFrom(start));
+      }
     }
 
     scanner.expectChar($lparen);
     whitespace();
-    var next = scanner.peekChar();
-    if (next == $lparen || next == $hash) {
-      var condition = _supportsCondition();
+    if (scanIdentifier("not")) {
       whitespace();
+      var condition = _supportsConditionInParens();
+      scanner.expectChar($rparen);
+      return SupportsNegation(condition, scanner.spanFrom(start));
+    } else if (scanner.peekChar() == $lparen) {
+      var condition = _supportsCondition();
       scanner.expectChar($rparen);
       return condition;
     }
 
-    if (next == $n || next == $N) {
-      var negation = _trySupportsNegation();
-      if (negation != null) {
+    // Unfortunately, we may have to backtrack here. The grammar is:
+    //
+    //       Expression ":" Expression
+    //     | InterpolatedIdentifier InterpolatedAnyValue?
+    //
+    // These aren't ambiguous because this `InterpolatedAnyValue` is forbidden
+    // from containing a top-level colon, but we still have to parse the full
+    // expression to figure out if there's a colon after it.
+    //
+    // We could avoid the overhead of a full expression parse by looking ahead
+    // for a colon (outside of balanced brackets), but in practice we expect the
+    // vast majority of real uses to be `Expression ":" Expression`, so it makes
+    // sense to parse that case faster in exchange for less code complexity and
+    // a slower backtracking case.
+    Expression name;
+    var nameStart = scanner.state;
+    var wasInParentheses = _inParentheses;
+    try {
+      name = expression();
+      scanner.expectChar($colon);
+    } on FormatException catch (_) {
+      scanner.state = nameStart;
+      _inParentheses = wasInParentheses;
+
+      var identifier = interpolatedIdentifier();
+      var operation = _trySupportsOperation(identifier, nameStart);
+      if (operation != null) {
         scanner.expectChar($rparen);
-        return negation;
+        return operation;
       }
+
+      // If parsing an expression fails, try to parse an
+      // `InterpolatedAnyValue` instead. But if that value runs into a
+      // top-level colon, then this is probably intended to be a declaration
+      // after all, so we rethrow the declaration-parsing error.
+      var contents = (InterpolationBuffer()
+            ..addInterpolation(identifier)
+            ..addInterpolation(_interpolatedDeclarationValue(
+                allowEmpty: true, allowSemicolon: true, allowColon: false)))
+          .interpolation(scanner.spanFrom(nameStart));
+      if (scanner.peekChar() == $colon) rethrow;
+
+      scanner.expectChar($rparen);
+      return SupportsAnything(contents, scanner.spanFrom(start));
     }
 
-    var name = expression();
-    scanner.expectChar($colon);
     whitespace();
     var value = expression();
     scanner.expectChar($rparen);
     return SupportsDeclaration(name, value, scanner.spanFrom(start));
   }
 
-  /// Tries to consume a negated supports condition.
+  /// If [interpolation] is followed by `"and"` or `"or"`, parse it as a supports operation.
   ///
-  /// Returns `null` if it fails.
-  SupportsNegation _trySupportsNegation() {
-    var start = scanner.state;
-    if (!scanIdentifier("not") || scanner.isDone) {
-      scanner.state = start;
-      return null;
-    }
+  /// Otherwise, return `null` without moving the scanner position.
+  SupportsOperation _trySupportsOperation(Interpolation interpolation, LineScannerState start) {
+    if (interpolation.contents.length != 1) return null;
+    var expression = interpolation.contents.first;
+    if (expression is! Expression) return null;
 
-    var next = scanner.peekChar();
-    if (!isWhitespace(next) && next != $lparen) {
-      scanner.state = start;
-      return null;
+    var beforeWhitespace = scanner.state;
+    whitespace();
+
+    SupportsOperation operation;
+    String operator;
+    while (lookingAtIdentifier()) {
+      if (operator != null) {
+        expectIdentifier(operator);
+      } else if (scanIdentifier("and")) {
+        operator = "and";
+      } else if (scanIdentifier("or")) {
+        operator = "or";
+      } else {
+        scanner.state = beforeWhitespace;
+        return null;
+      }
+
+      whitespace();
+      var right = _supportsConditionInParens();
+      operation = SupportsOperation(
+          operation ?? SupportsInterpolation(
+            expression as Expression, interpolation.span), right, operator, scanner.spanFrom(start));
+      whitespace();
     }
 
-    whitespace();
-    return SupportsNegation(
-        _supportsConditionInParens(), scanner.spanFrom(start));
+    return operation;
   }
 
   // ## Characters
diff --git a/lib/src/value/color.dart b/lib/src/value/color.dart
index 36261b897..c815954f8 100644
--- a/lib/src/value/color.dart
+++ b/lib/src/value/color.dart
@@ -98,8 +98,10 @@ class SassColor extends Value implements ext.SassColor {
   factory SassColor.hwb(num hue, num whiteness, num blackness, [num alpha]) {
     // From https://www.w3.org/TR/css-color-4/#hwb-to-rgb
     var scaledHue = hue % 360 / 360;
-    var scaledWhiteness = fuzzyAssertRange(whiteness, 0, 100, "whiteness") / 100;
-    var scaledBlackness = fuzzyAssertRange(blackness, 0, 100, "blackness") / 100;
+    var scaledWhiteness =
+        fuzzyAssertRange(whiteness, 0, 100, "whiteness") / 100;
+    var scaledBlackness =
+        fuzzyAssertRange(blackness, 0, 100, "blackness") / 100;
 
     var sum = scaledWhiteness + scaledBlackness;
     if (sum > 1) {
@@ -117,11 +119,8 @@ class SassColor extends Value implements ext.SassColor {
     // don't cache its values because we expect the memory overhead of doing so
     // to outweigh the cost of recalculating it on access. Instead, we eagerly
     // convert it to RGB and then convert back if necessary.
-    return SassColor.rgb(
-        toRgb(scaledHue + 1/3),
-        toRgb(scaledHue),
-        toRgb(scaledHue - 1/3),
-        alpha);
+    return SassColor.rgb(toRgb(scaledHue + 1 / 3), toRgb(scaledHue),
+        toRgb(scaledHue - 1 / 3), alpha);
   }
 
   SassColor._(this._red, this._green, this._blue, this._hue, this._saturation,
diff --git a/lib/src/visitor/async_evaluate.dart b/lib/src/visitor/async_evaluate.dart
index b7bbf74b1..69594f024 100644
--- a/lib/src/visitor/async_evaluate.dart
+++ b/lib/src/visitor/async_evaluate.dart
@@ -1806,6 +1806,11 @@ class _EvaluateVisitor
     } else if (condition is SupportsDeclaration) {
       return "(${await _evaluateToCss(condition.name)}: "
           "${await _evaluateToCss(condition.value)})";
+    } else if (condition is SupportsFunction) {
+      return "${await _performInterpolation(condition.name)}("
+          "${await _performInterpolation(condition.arguments)})";
+    } else if (condition is SupportsAnything) {
+      return "(${await _performInterpolation(condition.contents)})";
     } else {
       return null;
     }
diff --git a/lib/src/visitor/evaluate.dart b/lib/src/visitor/evaluate.dart
index 530301c11..4fcbb1de4 100644
--- a/lib/src/visitor/evaluate.dart
+++ b/lib/src/visitor/evaluate.dart
@@ -5,7 +5,7 @@
 // DO NOT EDIT. This file was generated from async_evaluate.dart.
 // See tool/grind/synchronize.dart for details.
 //
-// Checksum: 485fce53ba9f381973c25a69b193a681891be098
+// Checksum: ae80942bc5f7f9f4b92e7e4d46903578ea3b9a58
 //
 // ignore_for_file: unused_import
 
@@ -1797,6 +1797,11 @@ class _EvaluateVisitor
     } else if (condition is SupportsDeclaration) {
       return "(${_evaluateToCss(condition.name)}: "
           "${_evaluateToCss(condition.value)})";
+    } else if (condition is SupportsFunction) {
+      return "${_performInterpolation(condition.name)}("
+          "${_performInterpolation(condition.arguments)})";
+    } else if (condition is SupportsAnything) {
+      return "(${_performInterpolation(condition.contents)})";
     } else {
       return null;
     }
diff --git a/pubspec.yaml b/pubspec.yaml
index 120a1b2e1..cb1b1d1f5 100644
--- a/pubspec.yaml
+++ b/pubspec.yaml
@@ -1,5 +1,5 @@
 name: sass
-version: 1.28.0
+version: 1.29.0
 description: A Sass implementation in Dart.
 author: Sass Team
 homepage: https://github.com/sass/dart-sass
diff --git a/test/dart_api/value/color_test.dart b/test/dart_api/value/color_test.dart
index 4f88f60b8..aa5e189d4 100644
--- a/test/dart_api/value/color_test.dart
+++ b/test/dart_api/value/color_test.dart
@@ -130,22 +130,21 @@ void main() {
             equals(SassColor.hwb(210, 7.0588235294117645, 42)));
         expect(
             value.changeHwb(alpha: 0.5),
-            equals(
-                SassColor.hwb(210, 7.0588235294117645, 66.27450980392157, 0.5)));
+            equals(SassColor.hwb(
+                210, 7.0588235294117645, 66.27450980392157, 0.5)));
         expect(
-            value.changeHwb(
-                hue: 120, whiteness: 42, blackness: 42, alpha: 0.5),
+            value.changeHwb(hue: 120, whiteness: 42, blackness: 42, alpha: 0.5),
             equals(SassColor.hwb(120, 42, 42, 0.5)));
         expect(
-            value.changeHwb(whiteness: 50),
-            equals(SassColor.hwb(210, 43, 57)));
+            value.changeHwb(whiteness: 50), equals(SassColor.hwb(210, 43, 57)));
       });
 
       test("allows valid values", () {
         expect(value.changeHwb(whiteness: 0).whiteness, equals(0));
         expect(value.changeHwb(whiteness: 100).whiteness, equals(60.0));
         expect(value.changeHwb(blackness: 0).blackness, equals(0));
-        expect(value.changeHwb(blackness: 100).blackness, equals(93.33333333333333));
+        expect(value.changeHwb(blackness: 100).blackness,
+            equals(93.33333333333333));
         expect(value.changeHwb(alpha: 0).alpha, equals(0));
         expect(value.changeHwb(alpha: 1).alpha, equals(1));
       });
@@ -219,7 +218,10 @@ void main() {
     test("equals the same color", () {
       expect(value, equalsWithHash(SassColor.rgb(0x3E, 0x98, 0x3E)));
       expect(value, equalsWithHash(SassColor.hsl(120, 42, 42)));
-      expect(value, equalsWithHash(SassColor.hwb(120, 24.313725490196077, 40.3921568627451)));
+      expect(
+          value,
+          equalsWithHash(
+              SassColor.hwb(120, 24.313725490196077, 40.3921568627451)));
     });
   });
 
@@ -295,9 +297,9 @@ void main() {
     });
 
     test("allows valid values", () {
-      expect(SassColor.hwb(0, 0, 0, 0), equals(parseValue("rgba(255, 0, 0, 0)")));
-      expect(SassColor.hwb(4320, 100, 100, 1),
-          equals(parseValue("grey")));
+      expect(
+          SassColor.hwb(0, 0, 0, 0), equals(parseValue("rgba(255, 0, 0, 0)")));
+      expect(SassColor.hwb(4320, 100, 100, 1), equals(parseValue("grey")));
     });
 
     test("disallows invalid values", () {

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