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diff --git a/src/Hakyll/Core/Identifier.hs b/src/Hakyll/Core/Identifier.hs
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+-- | An identifier is a type used to uniquely identify a resource, target...
+--
+-- One can think of an identifier as something similar to a file path. An
+-- identifier is a path as well, with the different elements in the path
+-- separated by @/@ characters. Examples of identifiers are:
+--
+-- * @posts/foo.markdown@
+--
+-- * @index@
+--
+-- * @error/404@
+--
+-- The most important difference between an 'Identifier' and a file path is that
+-- the identifier for an item is not necesserily the file path.
+--
+-- For example, we could have an @index@ identifier, generated by Hakyll. The
+-- actual file path would be @index.html@, but we identify it using @index@.
+--
+-- @posts/foo.markdown@ could be an identifier of an item that is rendered to
+-- @posts/foo.html@. In this case, the identifier is the name of the source
+-- file of the page.
+--
+{-# LANGUAGE GeneralizedNewtypeDeriving #-}
+module Hakyll.Core.Identifier
+    ( Identifier (..)
+    , parseIdentifier
+    , toFilePath
+    ) where
+
+import Control.Arrow (second)
+import Data.Monoid (Monoid)
+
+import GHC.Exts (IsString, fromString)
+import System.FilePath (joinPath)
+
+-- | An identifier used to uniquely identify a value
+--
+newtype Identifier = Identifier {unIdentifier :: [String]}
+                   deriving (Eq, Ord, Monoid)
+
+instance Show Identifier where
+    show = toFilePath
+
+instance IsString Identifier where
+    fromString = parseIdentifier
+
+-- | Parse an identifier from a string
+--
+parseIdentifier :: String -> Identifier
+parseIdentifier = Identifier . filter (not . null) . split'
+  where
+    split' [] = [[]]
+    split' str = let (pre, post) = second (drop 1) $ break (== '/') str
+                 in pre : split' post
+
+-- | Convert an identifier to a relative 'FilePath'
+--
+toFilePath :: Identifier -> FilePath
+toFilePath = joinPath . unIdentifier