Lower priority for ATX headers to resolve conflict with HTML blocks

fix https://github.com/markdown-it/markdown-it/issues/772

CHANGELOG.md

@@ -6,6 +6,11 @@ The format is based on [Keep a Changelog](https://keepachangelog.com/en/1.0.0/),
 and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0.html).
 
 
+## [12.0.5] - WIP
+### Fixed
+- HTML block tags with `===` inside are no longer incorrectly interpreted as headers, #772.
+
+
 ## [12.0.4] - 2020-12-20
 ### Fixed
 - Fix crash introduced in `12.0.3` when processing strikethrough (`~~`) and similar plugins, #742.

lib/parser_block.js

@@ -19,9 +19,9 @@ var _rules = [
   [ 'hr',         require('./rules_block/hr'),         [ 'paragraph', 'reference', 'blockquote', 'list' ] ],
   [ 'list',       require('./rules_block/list'),       [ 'paragraph', 'reference', 'blockquote' ] ],
   [ 'reference',  require('./rules_block/reference') ],
+  [ 'html_block', require('./rules_block/html_block'), [ 'paragraph', 'reference', 'blockquote' ] ],
   [ 'heading',    require('./rules_block/heading'),    [ 'paragraph', 'reference', 'blockquote' ] ],
   [ 'lheading',   require('./rules_block/lheading') ],
-  [ 'html_block', require('./rules_block/html_block'), [ 'paragraph', 'reference', 'blockquote' ] ],
   [ 'paragraph',  require('./rules_block/paragraph') ]
 ];
 

test/fixtures/markdown-it/commonmark_extras.txt

@@ -635,3 +635,21 @@ baz</p>
 </blockquote>
 </blockquote>
 .
+
+Issue #772. Header rule should not interfere with html tags.
+.
+<!--
+==
+-->
+
+<pre>
+==
+</pre>
+.
+<!--
+==
+-->
+<pre>
+==
+</pre>
+.