position accross multiple node sets?

I'm trying to create a numbered list of items as plain text output from an XML file.  In the interest of simplicity I've created a stripped down version of the problem below.

Let's say I've got XML that looks like this:

<items>
	<book>XSLT Programmers Reference</book>
	<book>Beginning XSLT</book>
	<car>
		<model>camry</model>
		<year>2001</year>
	</car>
	<car>
		<model>Explorer</model>
		<year>2001</year>
	</car>
	<car>
		<model>accord</model>
		<year>1995</year>
	</car>
	<car>
		<model>escort</model>
		<year>1999</year>
	</car>
</items>


I've created two templates that use position() to number the items.  One that processes the <book/> nodes into:

0. XSLT Programmers Reference
1. Beginning XSLT

The other uses grouping on the car's <year/> node to output:

0. 2001
1. 1995
2. 1999

Making the sum-total of this template's output:

0. XSLT Programmers Reference
1. Beginning XSLT
0. 2001
1. 1995
2. 1999

What I actually need output is:

0. XSLT Programmers Reference
1. Beginning XSLT
2. 2001
3. 1995
4. 1999


I've got some ideas how to solve this, but I can't seem to get my head around them.

ideas?

thanks,
+jeff

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