Markdown reader: case-insensitive alert keywords (#11836)

The keywords (e.g. `TIP`) for GFM-style alerts need not be all caps.
This commit fixes that. It also adds the class `alert` to the produced
Divs to allow for namespacing.

This commit changes the emitted classes from the alert extension
of the basic Markdown reader to add the class `alert` to the
produced DIVs to allow for namespacing.

src/Text/Pandoc/Readers/Markdown.hs

@@ -819,7 +819,7 @@ blockQuote = do
     (do guardEnabled Ext_alerts
         case raw of
           (t:ts) | "[!" `T.isPrefixOf` t ->
-              case T.strip t of
+              case T.toUpper (T.strip t) of
                 "[!TIP]" -> pure (Just "tip", ts)
                 "[!WARNING]" -> pure (Just "warning", ts)
                 "[!IMPORTANT]" -> pure (Just "important", ts)
@@ -834,7 +834,7 @@ blockQuote = do
     case mbAlert of
       Nothing -> B.blockQuote <$> contents
       Just alert ->
-        (B.divWith ("", [alert], [])
+        (B.divWith ("", ["alert", alert], [])
           . (B.divWith ("", ["title"], []) (B.para (B.str (T.toTitle alert))) <>))
            <$> contents
 

test/command/9716.md

@@ -4,7 +4,7 @@
 > A suggestion.
 ^D
 [ Div
-    ( "" , [ "tip" ] , [] )
+    ( "" , [ "alert" , "tip" ] , [] )
     [ Div ( "" , [ "title" ] , [] ) [ Para [ Str "Tip" ] ]
     , Para [ Str "A" , Space , Str "suggestion." ]
     ]