diff --git a/lib/src/embedded/importer/file.dart b/lib/src/embedded/importer/file.dart
index 3e18452ff..fcbe72ce8 100644
--- a/lib/src/embedded/importer/file.dart
+++ b/lib/src/embedded/importer/file.dart
@@ -22,7 +22,7 @@ final class FileImporter extends ImporterBase {
       ..url = url.toString()
       ..fromImport = fromImport;
     var containingUrl = canonicalizeContext.containingUrlWithoutMarking;
-    if (containingUrl != null) {
+    if (containingUrl case var containingUrl?) {
       request.containingUrl = containingUrl.toString();
     }
     var response = dispatcher.sendFileImportRequest(request);
diff --git a/lib/src/embedded/importer/host.dart b/lib/src/embedded/importer/host.dart
index 2f2702fb1..4d68a5e10 100644
--- a/lib/src/embedded/importer/host.dart
+++ b/lib/src/embedded/importer/host.dart
@@ -36,7 +36,7 @@ final class HostImporter extends ImporterBase {
       ..url = url.toString()
       ..fromImport = fromImport;
     var containingUrl = canonicalizeContext.containingUrlWithoutMarking;
-    if (containingUrl != null) {
+    if (containingUrl case var containingUrl?) {
       request.containingUrl = containingUrl.toString();
     }
     var response = dispatcher.sendCanonicalizeRequest(request);
diff --git a/lib/src/importer/async.dart b/lib/src/importer/async.dart
index 00d29993a..d777d84f5 100644
--- a/lib/src/importer/async.dart
+++ b/lib/src/importer/async.dart
@@ -62,6 +62,9 @@ abstract class AsyncImporter {
   ///
   /// Subclasses should only access this from within calls to [canonicalize].
   /// Outside of that context, its value is undefined and subject to change.
+  ///
+  /// @nodoc
+  @internal
   @protected
   @nonVirtual
   CanonicalizeContext get canonicalizeContext => utils.canonicalizeContext;
diff --git a/lib/src/importer/canonicalize_context.dart b/lib/src/importer/canonicalize_context.dart
index f40a79229..05a3b3ea2 100644
--- a/lib/src/importer/canonicalize_context.dart
+++ b/lib/src/importer/canonicalize_context.dart
@@ -4,9 +4,13 @@
 
 import 'package:meta/meta.dart';
 
-class CanonicalizeContext {
+/// Contextual information used by importers' `canonicalize` method.
+@internal
+final class CanonicalizeContext {
+  /// Whether the Sass compiler is currently evaluating an `@import` rule.
   final bool fromImport;
 
+  /// The URL of the stylesheet that contains the current load.
   Uri? get containingUrl {
     _wasContainingUrlAccessed = true;
     return _containingUrl;
@@ -14,11 +18,17 @@ class CanonicalizeContext {
 
   final Uri? _containingUrl;
 
+  /// Returns the same value as [containingUrl], but doesn't mark it accessed.
   Uri? get containingUrlWithoutMarking => _containingUrl;
 
+  /// Whether [containingUrl] has been accessed.
+  ///
+  /// This is used to determine whether canonicalize result is cacheable.
+  ///
+  /// @nodoc
   @internal
   bool get wasContainingUrlAccessed => _wasContainingUrlAccessed;
-  bool _wasContainingUrlAccessed = false;
+  var _wasContainingUrlAccessed = false;
 
   CanonicalizeContext(this._containingUrl, this.fromImport);
 }