[xml] XInclude question

[gmxml saplings us]

I've been trying to get XInclude to work, but whenever I run

My base file format, stripped down, is
<gameconfig>
<TerrainTypeDefs>
<TerrainType type_name="volcano">
</TerrainType>
</TerrainTypeDefs>
<gameconfig>

That I can process just fine, and I get all the data.

What I want to do is move
<TerrainType type_name="volcano">
</TerrainType>

To it's own xml file, and rewite my main file as:
<gameconfig>
<TerrainTypeDefs>
<include href="terraintypes.xml">
</TerrainTypeDefs>
<gameconfig>

And functionally get the same result as above, so when I cycle through 
all the terraintypedefs I can pick up the new ones as well as the old 
ones.  I understand I may need to deal with an xinclude start and end 
tags(?) surrounding my import, but I can deal with that(my code throws 
an informational message for unidentified tags, so I would know if they 
were getting there without my specifying)

Everything is stored on the local filesystem, not a web server.

I tried setting the XINCLUDE options for the xmlCtxtReadFile function, 
that did not work but from reading the archives here, that may be 
because it does not support that option?

I've also tried:
     int includes = xmlXIncludeProcessFlags(gdconfigdoc, options);

With various options, it keeps coming back with 0 inclusions.

So I'm ready to give up on this item, but figured I'd ask here if there 
was something simple I'm missing.  Worst case, I can store all the data 
in one file.  I'd just like the option of storing the data in multiple 
files.