Restructure via grouping

How can I do the following restructuring? Do I need to use grouping?

Inside and outside of my <doc> node there are <fragment> nodes. I want
to collect them all and place them insde a new <fragments> tag.

So for this input:

<root>
	<doc>
		<fragment pos="1"/>
		<fragment pos="2"/>
		<fragment pos="3"/>
	</doc>
	<fragment pos="4"/>
	<fragment pos="5"/>
</root>

I would need the following output:
<root>
	<doc>
		<fragments>
			<fragment pos="1"/>
			<fragment pos="2"/>
			<fragment pos="3"/>
			<fragment pos="4"/>
			<fragment pos="5"/>
		</fragments>
	</doc>
</root>

I played around with generate-key() a little bit, but could not make it.
Can you help.

Thanks in advance.