xslt sort by two columns, where one is only partial

I have many nodes I wish to sort. - They all have a create date. - Some have an edit date to.

(update) Since no ansers I will add an example of en xml document to search

<page>
 <createdate>2010-01-05</createdate>
 <editdate>2010-01-07</editdate>
</page>
<page>
 <createdate>2010-01-06</createdate>
 <editdate></editdate>  (do not know is this row is there at all)
</page>
<page>
 <createdate>2010-01-07</createdate>
 <editdate>2010-01-10</editdate>
</page>

I would like a sort that order by开发者_运维技巧 "createdate and use "editdate" if it exist.

Can this be done in XSLT 1.0?

BR. Anders

UPDATE: SOLVED by solution given below

How about using a concatenation of editdate and createdate as the selection for the xsl:sort? like

 <xsl:for-each select="page">
   <xsl:sort select="concat(editdate, createdate)"/>
   <!-- do stuff -->
 </xsl:for-each>