Convert markdownlint library to an ECMAScript module, replace markdownlint-micromark with micromark, stop publishing (large) markdownlint-browser.js, see https://gist.github.com/sindresorhus/a39789f98801d908bbc7ff3ecc99d99c for guidance.

lib/md028.mjs

@@ -0,0 +1,39 @@
+// @ts-check
+
+import { addError } from "../helpers/helpers.cjs";
+import { filterByTypesCached } from "./cache.mjs";
+
+const ignoreTypes = new Set([ "lineEnding", "listItemIndent", "linePrefix" ]);
+
+/** @type {import("./markdownlint.mjs").Rule} */
+export default {
+  "names": [ "MD028", "no-blanks-blockquote" ],
+  "description": "Blank line inside blockquote",
+  "tags": [ "blockquote", "whitespace" ],
+  "parser": "micromark",
+  "function": function MD028(params, onError) {
+    for (const token of filterByTypesCached([ "blockQuote" ])) {
+      const errorLineNumbers = [];
+      const siblings = token.parent?.children || params.parsers.micromark.tokens;
+      for (let i = siblings.indexOf(token) + 1; i < siblings.length; i++) {
+        const sibling = siblings[i];
+        const { startLine, type } = sibling;
+        if (type === "lineEndingBlank") {
+          // Possible blank between blockquotes
+          errorLineNumbers.push(startLine);
+        } else if (ignoreTypes.has(type)) {
+          // Ignore invisible formatting
+        } else if (type === "blockQuote") {
+          // Blockquote followed by blockquote
+          for (const lineNumber of errorLineNumbers) {
+            addError(onError, lineNumber);
+          }
+          break;
+        } else {
+          // Blockquote not followed by blockquote
+          break;
+        }
+      }
+    }
+  }
+};