From ee5c361df0db8f264cf28f9baea863be23963ccc Mon Sep 17 00:00:00 2001
From: Matthew Lipski <matthewlipski@gmail.com>
Date: Thu, 26 Jun 2025 18:04:50 +0200
Subject: [PATCH 1/2] Fixed `bn-inline-content` class name being added to React
 custom block's inline content element whenever its content changed

---
 packages/react/src/schema/ReactBlockSpec.tsx | 10 ++++++++--
 1 file changed, 8 insertions(+), 2 deletions(-)

diff --git a/packages/react/src/schema/ReactBlockSpec.tsx b/packages/react/src/schema/ReactBlockSpec.tsx
index 9b15550d13..6ecf135d13 100644
--- a/packages/react/src/schema/ReactBlockSpec.tsx
+++ b/packages/react/src/schema/ReactBlockSpec.tsx
@@ -189,7 +189,10 @@ export function createReactBlockSpec<
                   editor={editor as any}
                   contentRef={(element) => {
                     ref(element);
-                    if (element) {
+                    if (
+                      element &&
+                      !element.classList.contains("bn-inline-content")
+                    ) {
                       element.className = mergeCSSClasses(
                         "bn-inline-content",
                         element.className,
@@ -268,7 +271,10 @@ export function createReactBlockSpec<
               editor={editor as any}
               contentRef={(element) => {
                 refCB(element);
-                if (element) {
+                if (
+                  element &&
+                  !element.classList.contains("bn-inline-content")
+                ) {
                   element.className = mergeCSSClasses(
                     "bn-inline-content",
                     element.className,

From 8d15c2ac0b8aa657eee8590bfb59667c7f28cbf2 Mon Sep 17 00:00:00 2001
From: Matthew Lipski <matthewlipski@gmail.com>
Date: Wed, 2 Jul 2025 14:09:29 +0200
Subject: [PATCH 2/2] Improved `mergeCSSClasses`

---
 packages/core/src/util/browser.ts            | 12 +++++++++++-
 packages/react/src/schema/ReactBlockSpec.tsx | 10 ++--------
 2 files changed, 13 insertions(+), 9 deletions(-)

diff --git a/packages/core/src/util/browser.ts b/packages/core/src/util/browser.ts
index 2a0a2905bd..118c138a48 100644
--- a/packages/core/src/util/browser.ts
+++ b/packages/core/src/util/browser.ts
@@ -13,7 +13,17 @@ export function formatKeyboardShortcut(shortcut: string, ctrlText = "Ctrl") {
 }
 
 export function mergeCSSClasses(...classes: (string | false | undefined)[]) {
-  return classes.filter((c) => c).join(" ");
+  return [
+    // Converts to & from set to remove duplicates.
+    ...new Set(
+      classes
+        .filter((c) => c)
+        // Ensures that if multiple classes are passed as a single string, they
+        // are split.
+        .join(" ")
+        .split(" "),
+    ),
+  ].join(" ");
 }
 
 export const isSafari = () =>
diff --git a/packages/react/src/schema/ReactBlockSpec.tsx b/packages/react/src/schema/ReactBlockSpec.tsx
index 6ecf135d13..9b15550d13 100644
--- a/packages/react/src/schema/ReactBlockSpec.tsx
+++ b/packages/react/src/schema/ReactBlockSpec.tsx
@@ -189,10 +189,7 @@ export function createReactBlockSpec<
                   editor={editor as any}
                   contentRef={(element) => {
                     ref(element);
-                    if (
-                      element &&
-                      !element.classList.contains("bn-inline-content")
-                    ) {
+                    if (element) {
                       element.className = mergeCSSClasses(
                         "bn-inline-content",
                         element.className,
@@ -271,10 +268,7 @@ export function createReactBlockSpec<
               editor={editor as any}
               contentRef={(element) => {
                 refCB(element);
-                if (
-                  element &&
-                  !element.classList.contains("bn-inline-content")
-                ) {
+                if (element) {
                   element.className = mergeCSSClasses(
                     "bn-inline-content",
                     element.className,