sorting by attribute

Can XSLT sort by attribute value?

<sender> 
	<a clli="200" b="20"/> 
	<a clli="100" b="10"/> 
	
      </sender> 

Output needed is
<wrapper>
  <a> @clli</a>
  <b> @b </b>
</wrapper>

I can sort by element content. 
REC says

<xsl:sort
  select = string-expression 
  
So, @clli is a string expression.

If I do a for-each on a/@clli
I can't get to the siblings, (no parent)
element a has no content so I can't sort on that.

I'm totally stuck on this one.
Can anyone help please.

Regards, DaveP




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