From cfa3d4ce4d58f5a777926c7e45e25b6d902199be Mon Sep 17 00:00:00 2001
From: Sarath Francis <sarathfrancis90@gmail.com>
Date: Tue, 30 Jun 2026 22:54:16 -0400
Subject: [PATCH] fix: treat a line of only tabs as a blank line between
 paragraphs

A line containing only tabs (or tabs mixed with spaces) is a blank line
per CommonMark, so it should break a paragraph. The paragraph rule only
checked for a spaces-only line ( +\n) in its continuation lookahead, so a
tab-only line was swallowed as a lazy continuation and the surrounding
text was merged into one paragraph. Widened it to [ \t]+\n to match tabs
too.
---
 src/rules.ts                             |  2 +-
 test/specs/new/blank_line_with_tabs.html |  4 ++++
 test/specs/new/blank_line_with_tabs.md   | 10 ++++++++++
 3 files changed, 15 insertions(+), 1 deletion(-)
 create mode 100644 test/specs/new/blank_line_with_tabs.html
 create mode 100644 test/specs/new/blank_line_with_tabs.md

diff --git a/src/rules.ts b/src/rules.ts
index c9bc07c5d6..997f9be52a 100644
--- a/src/rules.ts
+++ b/src/rules.ts
@@ -128,7 +128,7 @@ const lheadingGfm = edit(lheadingCore)
   .replace(/html/g, / {0,3}<[^\n>]+>\n/) // block html can interrupt
   .replace(/table/g, / {0,3}\|?(?:[:\- ]*\|)+[\:\- ]*\n/) // table can interrupt
   .getRegex();
-const _paragraph = /^([^\n]+(?:\n(?!hr|heading|lheading|blockquote|fences|list|html|table| +\n)[^\n]+)*)/;
+const _paragraph = /^([^\n]+(?:\n(?!hr|heading|lheading|blockquote|fences|list|html|table|[ \t]+\n)[^\n]+)*)/;
 const blockText = /^[^\n]+/;
 const _blockLabel = /(?!\s*\])(?:\\[\s\S]|[^\[\]\\])+/;
 const def = edit(/^ {0,3}\[(label)\]: *(?:\n[ \t]*)?([^<\s][^\s]*|<.*?>)(?:(?: +(?:\n[ \t]*)?| *\n[ \t]*)(title))? *(?:\n+|$)/)
diff --git a/test/specs/new/blank_line_with_tabs.html b/test/specs/new/blank_line_with_tabs.html
new file mode 100644
index 0000000000..83dc66c022
--- /dev/null
+++ b/test/specs/new/blank_line_with_tabs.html
@@ -0,0 +1,4 @@
+<p>foo</p>
+<p>bar</p>
+<p>baz</p>
+<p>qux</p>
diff --git a/test/specs/new/blank_line_with_tabs.md b/test/specs/new/blank_line_with_tabs.md
new file mode 100644
index 0000000000..a79bd0f899
--- /dev/null
+++ b/test/specs/new/blank_line_with_tabs.md
@@ -0,0 +1,10 @@
+---
+gfm: false
+---
+foo
+	
+bar
+
+baz
+	 	
+qux