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/md026.mjs

@@ -0,0 +1,46 @@
+// @ts-check
+
+import { addError, allPunctuationNoQuestion, endOfLineGemojiCodeRe,
+  endOfLineHtmlEntityRe, escapeForRegExp } from "../helpers/helpers.cjs";
+import { filterByTypesCached } from "./cache.mjs";
+
+/** @type {import("./markdownlint.mjs").Rule} */
+export default {
+  "names": [ "MD026", "no-trailing-punctuation" ],
+  "description": "Trailing punctuation in heading",
+  "tags": [ "headings" ],
+  "parser": "micromark",
+  "function": function MD026(params, onError) {
+    let punctuation = params.config.punctuation;
+    punctuation = String(
+      (punctuation === undefined) ? allPunctuationNoQuestion : punctuation
+    );
+    const trailingPunctuationRe =
+      new RegExp("\\s*[" + escapeForRegExp(punctuation) + "]+$");
+    const headings = filterByTypesCached([ "atxHeadingText", "setextHeadingText" ]);
+    for (const heading of headings) {
+      const { endColumn, endLine, text } = heading;
+      const match = trailingPunctuationRe.exec(text);
+      if (
+        match &&
+        !endOfLineHtmlEntityRe.test(text) &&
+        !endOfLineGemojiCodeRe.test(text)
+      ) {
+        const fullMatch = match[0];
+        const length = fullMatch.length;
+        const column = endColumn - length;
+        addError(
+          onError,
+          endLine,
+          `Punctuation: '${fullMatch}'`,
+          undefined,
+          [ column, length ],
+          {
+            "editColumn": column,
+            "deleteCount": length
+          }
+        );
+      }
+    }
+  }
+};