Allow raw latex commands starting with \start in Markdown.

Previously these weren't allowed because they were interpreted
as starting ConTeXt environments, even without a corresponding
\stop...

Closes #3558.

src/Text/Pandoc/Readers/Markdown.hs

@@ -1912,7 +1912,8 @@ inlineNote = try $ do
 rawLaTeXInline' :: PandocMonad m => MarkdownParser m (F Inlines)
 rawLaTeXInline' = try $ do
   guardEnabled Ext_raw_tex
-  lookAhead $ char '\\' >> notFollowedBy' (string "start") -- context env
+  lookAhead (char '\\')
+  notFollowedBy' rawConTeXtEnvironment
   RawInline _ s <- rawLaTeXInline
   return $ return $ B.rawInline "tex" s
   -- "tex" because it might be context or latex

test/command/3558.md

@@ -0,0 +1,8 @@
+```
+% pandoc -t native
+\startmulti
+hello
+\endmulti
+^D
+[Para [RawInline (Format "tex") "\\startmulti\n",Str "hello",SoftBreak,RawInline (Format "tex") "\\endmulti"]]
+```