Clarified field values in RstCustomRoles.

src/Text/Pandoc/Parsing.hs

@@ -854,6 +854,10 @@ data ParserState = ParserState
       stateMacros          :: [Macro],       -- ^ List of macros defined so far
       stateRstDefaultRole  :: String,        -- ^ Current rST default interpreted text role
       stateRstCustomRoles  :: M.Map String (String, Maybe String, Attr -> (String, Attr)), -- ^ Current rST custom text roles
+      -- Triple represents: 1) Base role, 2) Optional format (only for :raw:
+      -- roles), 3) Source language annotation for code (could be used to
+      -- annotate role classes too).
+
       stateWarnings        :: [String]       -- ^ Warnings generated by the parser
     }