Undo and redo behavior is inconsistent across browsers

Phenomenon

The undo and redo functionality (Ctrl+Z / Ctrl+Y or Cmd+Z / Cmd+Shift+Z) behaves differently across browsers. Some browsers undo individual keystrokes, while others undo larger operations. The undo stack may also be cleared unexpectedly.

Reproduction example

1. Create a contenteditable div.
2. Type several words.
3. Apply formatting (bold, italic).
4. Type more text.
5. Press Undo (Ctrl+Z or Cmd+Z) multiple times.
6. Observe what gets undone at each step.

Observed behavior

• In Edge on Windows, undo may revert entire formatting operations rather than individual keystrokes.
• The undo stack may be cleared when focus moves away from the contenteditable.
• Redo behavior may not work consistently after certain operations.

Expected behavior

• Undo should revert changes in a predictable order (typically most recent first).
• The undo stack should persist while the contenteditable remains in focus.
• Redo should restore undone changes in reverse order.