feat(theme-classic): extensible code block magic comment system (#7178)

website/docusaurus.config.js

@@ -378,6 +378,17 @@ const config = {
         // TODO after we have forked prism-react-renderer, we should tweak the
         // import order and fix it there
         additionalLanguages: ['java', 'markdown', 'latex'],
+        magicComments: [
+          {
+            className: 'theme-code-block-highlighted-line',
+            line: 'highlight-next-line',
+            block: {start: 'highlight-start', end: 'highlight-end'},
+          },
+          {
+            className: 'code-block-error-line',
+            line: 'This will error',
+          },
+        ],
       },
       image: 'img/docusaurus-soc.png',
       // metadata: [{name: 'twitter:card', content: 'summary'}],