Try this,
	name(preceding-sibling::*[1][name()='a1'])
Good luck,
Sreeni

-----Original Message-----
From: Hintz, David L [mailto:david.hintz@xxxxxxxxxxx] 
Sent: Thursday, April 23, 2009 11:01 AM
To: 'xsl-list@xxxxxxxxxxxxxxxxxxxxxx'
Subject:  Need test for preceding-sibling

Hi,

I have a structure like this:

<a1/>
<a2/>
<a1/>
<a2/>
<b/>
<c/>
<a2/>
<a1/>
<a2/>

I need to ensure that each <a2> has a preceding <a1>, although there may be
intervening tags.  I know that

	name(preceding-sibling::*[1]

gives me the name of the first preceding sibling, but how do I construct a
test that gives me only the first preceding <a1> or <a2> tag?

Thanks,
Dave