Profiling blocks of paragraphs

Our product ships on a number of different platforms, and thus our  
(mostly common) documentation uses profiling (with the arch  
attribute) so that we can build each variant as required.  Often,  
whole sections are different (e.g. installation instructions vary  
between Linux and Solaris versions of our product).

Now, we can't do this:

<section xml:id="Installation" arch = "Linux">
	<title>Installation</title>
	<para>...</para>
	<para>...</para>
	<para>...</para>
</section>

<section xml:id="Installation" arch = "Solaris">
	<title>Installation</title>
	<para>...</para>
	<para>...</para>
	<para>...</para>
</section>

...because you can't have two elements with the same xml:id, but we  
need the xml:id to be consistent so that our cross-references work  
cleanly.

What I want to do is this:

<section xml:id="Installation">
	<title>Installation</title>
	<contentgroup  arch = "Linux">
		<para>...</para>
		<para>...</para>
		<para>...</para>
	</contentgroup>

	<contentgroup  arch = "Solaris">
		<para>...</para>
		<para>...</para>
		<para>...</para>
	</contentgroup>
</section>

But as far as I can see, there is no <contentgroup> equivalent, so it  
looks like we'll have to do this:

<section xml:id="Installation">
	<title>Installation</title>
	<para arch = "Linux">...</para>
	<para arch = "Linux">...</para>
	<para arch = "Linux">...</para>
	<para arch = "Solaris">...</para>
	<para arch = "Solaris">...</para>
	<para arch = "Solaris">...</para>
</section>

Which is cumbersome and likely to be bug-prone over time.  Am I  
missing anything in the docbook spec, or is there really nothing that  
fulfils the requirement?

Thanks,

Geraint North
Principal Engineer
Transitive