[temporary] Clarify comment

src/Xrefcheck/System.hs

@@ -49,6 +49,10 @@ askWithinCI = lookupEnv "CI" <&> \case
 -- This type exist in contrast to 'FilePath' which, in this project,
 -- is used for platform-dependent file paths and related filesystem
 -- IO operations.
+--
+-- Note that `RelPosixLink` may contain `\` characters, but they are
+-- considered as part of the filename instead of denoting a path
+-- separator.
 newtype RelPosixLink = RelPosixLink
   { unRelPosixLink :: Text
   } deriving newtype (Show, Eq, Ord, NFData, Buildable, Pretty)
@@ -72,6 +76,8 @@ RelPosixLink a </> RelPosixLink b =
 -- Get the platform-dependent file path from a 'RelPosixLink'
 -- considered as relative to another given platform-dependent
 -- 'FilePath'.
+--
+-- In Windows, every `\` occurrence will be replaced by `/`.
 filePathFromRoot :: FilePath -> RelPosixLink -> FilePath
 filePathFromRoot rootPath = (rootPath FP.</>)
   . toString