Merge branch 'main' into fix-3729

Author: atsansone

src/_11ty/plugins/highlight.js

@@ -46,6 +46,12 @@ export async function configureHighlighting(markdown) {
     const token = tokens[index];
 
     const splitTokenInfo = token.info.match(/(\S+)\s?(.*?)$/m);
+
+    if (!splitTokenInfo) {
+      throw new Error('Each Markdown code block should specify a language ' +
+          'after the opening backticks like: ```dart.');
+    }
+
     const language = splitTokenInfo.length > 1 ? splitTokenInfo[1] : '';
     const attributes = splitTokenInfo.length > 2 ? splitTokenInfo[2] : '';