Markdown reader: fix regression with example list references.

This affects example list references followed by dashes.
Introduced by commit b8d17f7.
Closes #6855.

src/Text/Pandoc/Parsing.hs

@@ -798,7 +798,11 @@ exampleNum :: Stream s m Char
            => ParserT s ParserState m (ListNumberStyle, Int)
 exampleNum = do
   char '@'
-  lab <- T.pack <$> many (alphaNum <|> satisfy (\c -> c == '_' || c == '-'))
+  lab <- mconcat . map T.pack <$>
+                    many (many1 alphaNum <|>
+                          try (do c <- char '_' <|> char '-'
+                                  cs <- many1 alphaNum
+                                  return (c:cs)))
   st <- getState
   let num = stateNextExample st
   let newlabels = if T.null lab

src/Text/Pandoc/Readers/Markdown.hs

@@ -1544,7 +1544,11 @@ exampleRef :: PandocMonad m => MarkdownParser m (F Inlines)
 exampleRef = try $ do
   guardEnabled Ext_example_lists
   char '@'
-  lab <- many1Char (alphaNum <|> oneOf "-_")
+  lab <- mconcat . map T.pack <$>
+                    many (many1 alphaNum <|>
+                          try (do c <- char '_' <|> char '-'
+                                  cs <- many1 alphaNum
+                                  return (c:cs)))
   return $ do
     st <- askF
     return $ case M.lookup lab (stateExamples st) of

test/command/6855.md

@@ -0,0 +1,12 @@
+```
+% pandoc -t markdown
+(@a) one
+(@b) two
+
+See (@a--@b)
+^D
+(1) one
+(2) two
+
+See (1--2)
+```