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/md027.mjs

@@ -0,0 +1,40 @@
+// @ts-check
+
+import { addErrorContext } from "../helpers/helpers.cjs";
+import { filterByTypesCached } from "./cache.mjs";
+
+/** @type {import("./markdownlint.mjs").Rule} */
+export default {
+  "names": [ "MD027", "no-multiple-space-blockquote" ],
+  "description": "Multiple spaces after blockquote symbol",
+  "tags": [ "blockquote", "whitespace", "indentation" ],
+  "parser": "micromark",
+  "function": function MD027(params, onError) {
+    const { tokens } = params.parsers.micromark;
+    for (const token of filterByTypesCached([ "linePrefix" ])) {
+      const parent = token.parent;
+      const codeIndented = parent?.type === "codeIndented";
+      const siblings = parent?.children || tokens;
+      if (
+        !codeIndented &&
+        (siblings[siblings.indexOf(token) - 1]?.type === "blockQuotePrefix")
+      ) {
+        const { startColumn, startLine, text } = token;
+        const { length } = text;
+        const line = params.lines[startLine - 1];
+        addErrorContext(
+          onError,
+          startLine,
+          line,
+          undefined,
+          undefined,
+          [ startColumn, length ],
+          {
+            "editColumn": startColumn,
+            "deleteCount": length
+          }
+        );
+      }
+    }
+  }
+};