However, I cannot test some special cases with this unfortunately. The cases are, keyboard events on non-editable element. For example, when non-editable element has focus, composition won't be started usually. Therefore, keyboard events for a dead key sequence may be different if focus is in readonly editor.
So, I hope that there is a checkbox to toggle readonly or editable.
I really love Keyboard Event Viewer: https://w3c.github.io/uievents/tools/key-event-viewer.html
However, I cannot test some special cases with this unfortunately. The cases are, keyboard events on non-editable element. For example, when non-editable element has focus, composition won't be started usually. Therefore, keyboard events for a dead key sequence may be different if focus is in readonly editor.
So, I hope that there is a checkbox to toggle readonly or editable.