formatblock on selection with a contenteditable="false" child.
| <h1>
|   <i>
|     "\n        <#selection-anchor>Will select from here\n        "
|   <br>
|   <i>
|     "\n        until here.<#selection-focus>\n    "
| <div>
|   contenteditable="false"
|   "\n            over this contenteditable=false div\n        "