media10.mysite.com
 media11.mysite.com
 media12.mysite.com
 media13.mysite.com
 media14.mysite.com
 media15.mysite.com
 media1.mysite.com
 media2.mysite.com

It looks like you want to do a numeric sort not a lexical sort,
something like

 <xsl:sort data-type="number"
           select="substring-before(substring-after(.,'media'),'.')"/>



David

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