MutationObserver may interfere with contenteditable editing

Phenomenon

When a MutationObserver is attached to a contenteditable element or its parent, the observer callbacks may interfere with editing performance. Frequent DOM mutations during typing can trigger many observer callbacks, causing lag or jank.

Reproduction example

1. Create a contenteditable div.
2. Attach a MutationObserver that logs all mutations.
3. Type text rapidly in the contenteditable.
4. Observe performance and any lag.
5. Compare with typing without the observer.

Observed behavior

• In Safari on macOS, MutationObserver callbacks can cause performance issues.
• Rapid typing may trigger many mutations and callbacks.
• The UI may lag or become unresponsive.
• Performance degrades with complex observer logic.

Expected behavior

• MutationObserver should not significantly impact editing performance.
• Or, there should be a way to batch mutations.
• Callbacks should be optimized for contenteditable use cases.