gtksourceview: handling multiple languages

I use gtksourceview in my application's script editor and find it 
very useful -- many thanks to the developers!  Right now I'm trying 
to do something a bit more ambitious than what I've attempted to 
date, and I'd appreciate some advice.

The econometrics program I work on, gretl, supports embedding of 
"foreign" scripts, with a mechanism to shuttle data and results 
between gretl and the foreign program (which might be, e.g., python, 
R, or octave). The set-up looks like this (taking R as an example):

<initial gretl statements>
foreign language=R [ --send-data ]
   <R statements>
end foreign
<more gretl statements>

The issue, then, is switching from "native gretl" syntax 
highlighting in the main script, to appropriate highlighting for the 
statements inside the "foreign" block, and then back to native gretl 
when the block ends.

I gather that gtksourceview can handle this, and I'm using the 
treatment of javascript inside html (in html.lang) as a template. 
Here's my attempt at the relevant gtksourceview stanza (for R in 
particular, though it would be nice to be able to generalize it) in 
my gretl.lang file:

<context id="foreign-R" class="no-spell-check" style-inside="true">
   <start>^\s*foreign\s+language=R.*</start>
   <end>^\s*end\s+foreign</end>

   <include>
     <context id="R-code" extend-parent="false">
       <start>^</start>
       <include>
         <context ref="r:r"/>
      </include>
     </context>
   </include>
</context>

This works partially: it switches to R highlighting within the block 
OK, but (a) it leaves the "foreign..." and "end foreign" lines 
unhighlighted (I want them to be highlighted since both "foreign" 
and "end" are gretl keywords) and (b) the R-style highlighting 
bleeds over the end of the "foreign" block and affects everything 
from that point on in the main gretl script.

I suppose I'm missing something fairly basic here. Any suggestions? 
I can provide more detail on the gretl.lang file, but the basic 
version (prior to my attempt to handle "foreign" properly) can be 
found at

http://users.wfu.edu/cottrell/gretl/gretl.lang

-- 
Allin Cottrell
Department of Economics
Wake Forest University