This tests selecting all, copying, and pasting a content that starts and ends with canvas elements.
To manually test, copy and paste the content below:

Before paste:
| "\n"
| <#selection-anchor>
| <canvas>
|   height="100"
|   style="border: 1px solid black"
|   width="100"
| "\nsome text\n"
| <canvas>
|   height="100"
|   style="border: 1px solid black"
|   width="100"
| "\nsome more text\n"
| <canvas>
|   height="100"
|   style="border: 1px solid black"
|   width="100"
| <#selection-focus>
| "\n"

After paste:
| <canvas>
|   height="100"
|   style="border: 1px solid black;"
|   width="100"
| " "
| "some text"
| " "
| <canvas>
|   height="100"
|   style="border: 1px solid black;"
|   width="100"
| " "
| "some more text"
| " "
| <canvas>
|   height="100"
|   style="border: 1px solid black;"
|   width="100"
| <#selection-caret>
| <br>