[xsl] move tag up to level

["alex v." <alex.vett@xxxxxxxxx>]

Hi,
I have to transform a structure like this:

<root>
<a>mixed content like text and tags
<b>other mixed content</b>
mixed content also here
</a></root>

in another like:

<root>
<a>mixed content like text and tags</a>
<b>other mixed content</b>
<a>mixed content also here</a>
</root>

Tag 'a' is closed before '<b>' and then reopen follow '</b>'.
Also tag 'b' is promote at level of tag 'a'.

Can someone tell me how to do this?

Thanks,
~alex