diff --git a/core/inject.ts b/core/inject.ts
index e6d97b118..1fd3d58d6 100644
--- a/core/inject.ts
+++ b/core/inject.ts
@@ -47,8 +47,8 @@ export function inject(
     containerElement = container;
   }
   // Verify that the container is in document.
-  if (!containerElement || !dom.containsNode(document, containerElement)) {
-    throw Error('Error: container is not in current document.');
+  if (!document.contains(containerElement)) {
+    throw Error('Error: container is not in current document');
   }
   const options = new Options(opt_options || {} as BlocklyOptions);
   const subContainer = (document.createElement('div'));
@@ -56,7 +56,7 @@ export function inject(
   subContainer.tabIndex = 0;
   aria.setState(subContainer, aria.State.LABEL, Msg['WORKSPACE_ARIA_LABEL']);
 
-  containerElement.appendChild(subContainer);
+  containerElement!.appendChild(subContainer);
   const svg = createDom(subContainer, options);
 
   // Create surfaces for dragging things. These are optimizations
diff --git a/core/utils/dom.ts b/core/utils/dom.ts
index 363000480..6fe450351 100644
--- a/core/utils/dom.ts
+++ b/core/utils/dom.ts
@@ -7,6 +7,7 @@
 import * as goog from '../../closure/goog/goog.js';
 goog.declareModuleId('Blockly.utils.dom');
 
+import * as deprecation from './deprecation.js';
 import type {Svg} from './svg.js';
 
 
@@ -33,7 +34,6 @@ export enum NodeType {
   ELEMENT_NODE = 1,
   TEXT_NODE = 3,
   COMMENT_NODE = 8,
-  DOCUMENT_POSITION_CONTAINED_BY = 16
 }
 
 /** Temporary cache of text widths. */
@@ -160,11 +160,13 @@ export function insertAfter(newNode: Element, refNode: Element) {
  * @param parent The node that should contain the other node.
  * @param descendant The node to test presence of.
  * @returns Whether the parent node contains the descendant node.
+ * @deprecated Use native 'contains' DOM method.
  */
 export function containsNode(parent: Node, descendant: Node): boolean {
-  return !!(
-      parent.compareDocumentPosition(descendant) &
-      NodeType.DOCUMENT_POSITION_CONTAINED_BY);
+  deprecation.warn(
+      'Blockly.utils.dom.containsNode', 'version 10', 'version 11',
+      'Use native "contains" DOM method');
+  return parent.contains(descendant);
 }
 
 /**
diff --git a/core/workspace_svg.ts b/core/workspace_svg.ts
index c5a07ab04..735573e31 100644
--- a/core/workspace_svg.ts
+++ b/core/workspace_svg.ts
@@ -641,8 +641,8 @@ export class WorkspaceSvg extends Workspace implements IASTNodeLocationSvg {
     let x = 0;
     let y = 0;
     let scale = 1;
-    if (dom.containsNode(this.getCanvas(), element) ||
-        dom.containsNode(this.getBubbleCanvas(), element)) {
+    if (this.getCanvas().contains(element) ||
+        this.getBubbleCanvas().contains(element)) {
       // Before the SVG canvas, scale the coordinates.
       scale = this.scale;
     }