Handle invalid markup

src/index.js

@@ -32,7 +32,7 @@ export default {
           return el('sparkle')
           break
         default:
-          return token.raw
+          return `$[${token.markup} ${this.parser.parseInline(token.tokens)}]`
         }
       },
     },

test/index.test.js

@@ -11,4 +11,9 @@ describe('marked-mfm', () => {
     marked.use(markedMfm)
     expect(marked('$[twitch twitch $[sparkle sparkle]]')).toBe('<p><span style="display: inline-block" class="twitch">twitch <span style="display: inline-block" class="sparkle">sparkle</span></span></p>\n')
   })
+
+  test('invalid', () => {
+    marked.use(markedMfm)
+    expect(marked('$[invalid $[x2 test]]')).toBe('<p>$[invalid <span style="display: inline-block" class="x2">test</span>]</p>\n')
+  })
 })