Going to "above root node" by pressing Backspace when the list of top-level nodes are displayed in XML structure popup window (Ctrl+F12) will show the root node item (together with useless double-dots). While the list of the top-level nodes does not have double-dots to go upper in hierarchy (but Backspace still works).

Note also that it is possible to get the similar display by pressing Ctrl+F12 when cursor is immediately after the top-level node closing tag, like:

<sqlMap>
    <resultMap>
    ...
    </resultMap>|
</sqlMap>

or when it is before the opening root node tag:

|<sqlMap>
    <resultMap>
    ...
    </resultMap>
</sqlMap>

However when it's above the root node for example:

|
<sqlMap>
    <resultMap>
    ...
    </resultMap>
</sqlMap>

Ctrl+F12 dislpays popup with the list of top-level nodes (<resultMap>)

(hope the explanation is clear enough :) )

Issue was resolved