This tests inserting h6 inside h6 doesn't end up in a nested h6'es.
All three lines should be of the same font size. Each line should be of the said color.

After paste:
| "
"
| <h6>
|   id="target"
|   style="color: blue"
|   "Blue Line 1"
|   <br>
| <h6>
|   "Black Line<#selection-caret>"
| <h6>
|   style="color: blue"
|   "Blue Line 2"
| "
"

After innerHTML = innerHTML:
| "
"
| <h6>
|   id="target"
|   style="color: blue"
|   "Blue Line 1"
|   <br>
| <#selection-caret>
| <h6>
|   "Black Line"
| <h6>
|   style="color: blue"
|   "Blue Line 2"
| "
"