Created attachment 215028 [details]
If there are non-editable elements on the start or the end of an editable block,
"select all" operation doesn't select anything.
On the attached test case,
if you "select all" by Ctrl+A on the yellow editable area below 3), you can see the whole text in the editable block are selected.
However, if you "select all" on the editable area below 1) or 2), you can see nothing is selected.
On Firefox, for both 1) and 2), the whole text in the editable block are selected, and I think it's right.