Explain file for Geo searches

I need to create an SRW Explain file for the Meta Search
application underlying the Science.Gov Web site. My draft
is at http://www.search.gov/scienceExplain.xml

It is our intent to have this SRW also support the Geo
search on a bounding box of coordinates. For example,
the CQL to look for titles with "water" in Texas is:

   (dc.title any "water")and(geo.coordinates geo.overlap/geo.coordinate 
"-106.7,25.8,-93.5,36.5")

I see how to encode the index "geo.coordinates" in
the Explain file, but I don't see how to encode
"geo.overlap" and "geo.coordinate". Can anyone
help me here?

Eliot