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/md012.mjs

@@ -0,0 +1,40 @@
+// @ts-check
+
+import { addErrorDetailIf } from "../helpers/helpers.cjs";
+import { addRangeToSet } from "../helpers/micromark-helpers.cjs";
+import { filterByTypesCached } from "./cache.mjs";
+
+/** @type {import("./markdownlint.mjs").Rule} */
+export default {
+  "names": [ "MD012", "no-multiple-blanks" ],
+  "description": "Multiple consecutive blank lines",
+  "tags": [ "whitespace", "blank_lines" ],
+  "parser": "micromark",
+  "function": function MD012(params, onError) {
+    const maximum = Number(params.config.maximum || 1);
+    const { lines } = params;
+    const codeBlockLineNumbers = new Set();
+    for (const codeBlock of filterByTypesCached([ "codeFenced", "codeIndented" ])) {
+      addRangeToSet(codeBlockLineNumbers, codeBlock.startLine, codeBlock.endLine);
+    }
+    let count = 0;
+    for (const [ lineIndex, line ] of lines.entries()) {
+      const inCode = codeBlockLineNumbers.has(lineIndex + 1);
+      count = (inCode || (line.trim().length > 0)) ? 0 : count + 1;
+      if (maximum < count) {
+        addErrorDetailIf(
+          onError,
+          lineIndex + 1,
+          maximum,
+          count,
+          undefined,
+          undefined,
+          undefined,
+          {
+            "deleteCount": -1
+          }
+        );
+      }
+    }
+  }
+};