test.rb

dell_region = case real_domain
when /^(aus).dell.com/
  'AMER'
when /^(lon).dell.com/
  'EMEA'
else
 'UNKNOWN'
end

Facter.add('dell_location') do
  confine :kernel => :linux
  setcode do
    ## Logic to pull from dell.cfg
  end
end

Facter.add('dell_location') do
  confine :kernel => :windows
  setcode do
    ## Logic to pull from Registry
  end
end

Facter.add('dell_combined') do
  case Facter.value(:kernel)
  when 'Linux'
    # Do Linux logic here
    some_var = do_linux_lookup('foo')
  when 'windows'
    # Do Windows logic here
    some_var = do_windows_lookup('foo')
  end
  
  setcode do
    # Use the variable above and set the fact
  end
end

  
Facter.add('dell_region') do
  confine :kernel => :linux
  setcode do
    # Get location from Fact
    location = Facter.value(:location)

    # Now do things...
  end
end