When document A.gnumeric references and external document B.gnumeric, there
should be a valid relative path syntax for doing so.  e.g. allow

   [./B.gnumeric]sheet1!A5

in place of

   [/home/joe/MyDocs/B.gnumeric]sheet1!A5

where A.gnumeric (which is referencing B.gnumeric) also resides in directory 
/home/joe/MyDocs/.

There may be a semantics difficulty here.  What is the path relative to?  The
current working directory, or the directory where A.gnumeric resides.
They might not be the same if we launched gnumeric as follows...

   gumeric MyDocs/B.gnumeric &

I prefer the latter option.  i.e. relative to the file making the reference.

Rational:

I want to ship one interactive sheets which references several read only sheets
as a tarball without requiring the tarball be extracted in a 'magic' directory,
or requiring extensive editing of external references.