Is it possible to split chapters ?

[Kate.Wringe@ianywhere.com]

Hello,

We are using  docbook 4.2 with
our own customizations and our authoring tool is  XMetaL 5.0.

Currently we have a very large chapter,
largechapter.xml,  that contains reference material.
This chapter is divided into  sect1s.
 For various reasons, we'd like
to split up  the contents of largechapter.xml
into three files/entities and insert the 
entities into the largechapter.xml.

What we've done is created three files
that contain a list of sect1s.
For example file1.xml 's hierarchy looks
like the following:
<sect1>
        referenceA
material
</sect1>
<sect1>
        referenceB
material
</sect1>
...

We have no problem inserting an entity
for file1.xml into largechapter.xml and validating
largechaper.xml. The problem is that
we can't validate file1.xml on its own, because
it does not contain an over-arching
root. As a result, it is difficult for us to edit 
file1.xml.  Is there a tag that
we could use that would fit within the chapter tag and would
accept sect1s? Or is there another way
to do this?

I know that an easy solution would be
to convert all the current sect1s in file1.xml
to sect2s and use one sect1. We'd prefer
not to do this as it would add an 
extra level for our users to drill down
through. 

Any suggestions welcome!

Thank you,
Kate