ghc and hierarchical module names

[Tim Barbour]

The release notes for ghc 5.02.1 say:

   1.4.4. New experimental features

        Partial support for hierarchical module names.

- but I could not find a document describing how to use this feature.

Is it possible to use hierarchical module names with ghc at present, and if so,
how does one write and use a hierarchically-named module ?

Tim
-- 
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 safety deserve neither liberty nor safety." -- Benjamin Franklin