+
+-- | A typeclass for XML types that can be converted into an
+-- associated database type. The story behind this is long, but
+-- basically, we need to different types most XML thingies we're
+-- going to import: a database type and an XML type.
+--
+-- Both Groundhog and HXT are very particular about the types that
+-- they can use, and there's no way to reuse e.g. a type that HXT
+-- can pickle in Groundhog. This typeclass gives us a standard way
+-- to get the database type from the XML type that we have to define
+-- for HXT.
+--
+class FromXml a where
+ -- | Each instance @a@ must declare its associated database type @Db a@.
+ type Db a :: *
+
+ -- | And provide a function for getting a @Db a@ out of an @a@.
+ from_xml :: a -> Db a
+
+
+-- | Represents the DTD filename (\"SYSTEM\") part of the DOCTYPE
+-- definition.
+newtype DtdName = DtdName String
+