Update MD018/MD019/MD020/MD021 to look specifically for "space" characters (space or tab) instead of RegExp's "\s" characters per CommonMark specification (fixes #367).

demo/markdownlint-browser.js

@@ -2368,7 +2368,7 @@ module.exports = {
     "function": function MD018(params, onError) {
         forEachLine(lineMetadata(), function (line, lineIndex, inCode) {
             if (!inCode &&
-                /^#+[^#\s]/.test(line) &&
+                /^#+[^# \t]/.test(line) &&
                 !/#\s*$/.test(line) &&
                 !line.startsWith("#️⃣")) {
                 var hashCount = /^#+/.exec(line)[0].length;
@@ -2402,7 +2402,7 @@ module.exports = {
         filterTokens(params, "heading_open", function (token) {
             if (headingStyleFor(token) === "atx") {
                 var line = token.line, lineNumber = token.lineNumber;
-                var match = /^(#+)(\s{2,})(?:\S)/.exec(line);
+                var match = /^(#+)([ \t]{2,})(?:\S)/.exec(line);
                 if (match) {
                     var hashLength = match[1]["length"], spacesLength = match[2]["length"];
                     addErrorContext(onError, lineNumber, line.trim(), null, null, [1, hashLength + spacesLength + 1], {
@@ -2436,7 +2436,7 @@ module.exports = {
     "function": function MD020(params, onError) {
         forEachLine(lineMetadata(), function (line, lineIndex, inCode) {
             if (!inCode) {
-                var match = /^(#+)(\s*)([^#]*?[^#\\])(\s*)((?:\\#)?)(#+)(\s*)$/.exec(line);
+                var match = /^(#+)([ \t]*)([^#]*?[^#\\])([ \t]*)((?:\\#)?)(#+)(\s*)$/.exec(line);
                 if (match) {
                     var leftHash = match[1], leftSpaceLength = match[2]["length"], content = match[3], rightSpaceLength = match[4]["length"], rightEscape = match[5], rightHash = match[6], trailSpaceLength = match[7]["length"];
                     var leftHashLength = leftHash.length;
@@ -2487,7 +2487,7 @@ module.exports = {
         filterTokens(params, "heading_open", function (token) {
             if (headingStyleFor(token) === "atx_closed") {
                 var line = token.line, lineNumber = token.lineNumber;
-                var match = /^(#+)(\s+)([^#]+?)(\s+)(#+)(\s*)$/.exec(line);
+                var match = /^(#+)([ \t]+)([^#]+?)([ \t]+)(#+)(\s*)$/.exec(line);
                 if (match) {
                     var leftHash = match[1], leftSpaceLength = match[2]["length"], content = match[3], rightSpaceLength = match[4]["length"], rightHash = match[5], trailSpaceLength = match[6]["length"];
                     var left = leftSpaceLength > 1;

lib/md018.js

@@ -12,7 +12,7 @@ module.exports = {
   "function": function MD018(params, onError) {
     forEachLine(lineMetadata(), (line, lineIndex, inCode) => {
       if (!inCode &&
-        /^#+[^#\s]/.test(line) &&
+        /^#+[^# \t]/.test(line) &&
         !/#\s*$/.test(line) &&
         !line.startsWith("#️⃣")) {
         const hashCount = /^#+/.exec(line)[0].length;

lib/md019.js

@@ -13,7 +13,7 @@ module.exports = {
     filterTokens(params, "heading_open", (token) => {
       if (headingStyleFor(token) === "atx") {
         const { line, lineNumber } = token;
-        const match = /^(#+)(\s{2,})(?:\S)/.exec(line);
+        const match = /^(#+)([ \t]{2,})(?:\S)/.exec(line);
         if (match) {
           const [
             ,

lib/md020.js

@@ -13,7 +13,7 @@ module.exports = {
     forEachLine(lineMetadata(), (line, lineIndex, inCode) => {
       if (!inCode) {
         const match =
-          /^(#+)(\s*)([^#]*?[^#\\])(\s*)((?:\\#)?)(#+)(\s*)$/.exec(line);
+          /^(#+)([ \t]*)([^#]*?[^#\\])([ \t]*)((?:\\#)?)(#+)(\s*)$/.exec(line);
         if (match) {
           const [
             ,

lib/md021.js

@@ -13,7 +13,7 @@ module.exports = {
     filterTokens(params, "heading_open", (token) => {
       if (headingStyleFor(token) === "atx_closed") {
         const { line, lineNumber } = token;
-        const match = /^(#+)(\s+)([^#]+?)(\s+)(#+)(\s*)$/.exec(line);
+        const match = /^(#+)([ \t]+)([^#]+?)([ \t]+)(#+)(\s*)$/.exec(line);
         if (match) {
           const [
             ,

test/headings-with-invalid-spaces.md

@@ -0,0 +1,42 @@
+# Headings with invalid spaces
+
+## Normal space
+
+##  Normal outer non-breaking inner space
+
+## Non-breaking space {MD018}
+
+##	Tab
+
+## Normal space (both) ##
+
+##  Normal outer non-breaking inner space (both)  ##
+
+## Non-breaking space (left) {MD020} ##
+
+##	Tab (left) ##
+
+## Non-breaking space (right) {MD020} ##
+
+## Tab (right)	##
+
+##  Extra normal space {MD019}
+
+##  Extra non-breaking space {MD018}
+
+##		Extra Tab {MD019}
+
+##  Extra Normal space (both) {MD021}  ##
+
+##  Extra non-breaking space (left) {MD020} ##
+
+##		Extra tab (left) {MD021} ##
+
+## Extra non-breaking space (right) {MD020}  ##
+
+## Extra tab (right) {MD021}		##
+
+<!-- markdownlint-configure-file {
+    "heading-style": false,
+    "no-hard-tabs": false
+} -->