xsl:grouping for multiple categories?

i have this structure of xml:

<root>
        <item>
                <category></category>
                <title></title>
                <url></url>
                <description></description>
        </item>
               <item>
                <category></category>
                <title></title>
                <url></url>
                <description></description>
        </item>

</root>

Is it possible to group items according to several categories? For example, 
an item may be under the category "today's news" but also "relevant 
technology":
<item>
                <category>today's news</category>
                               <category>relevant technology</category>
                <title></title>
                <url></url>
                <description></description>
</item>

given i have a key <xsl:key name="items-by-category" match="item" 
use="category" />, would this create 2 key value pairs for one item?
I tried putting more than one category for each item but in the output, the 
whole category disappeared!!
any help would be greatly appreciated
james

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