Unescape any backslash escaped inline raw HTML

Fixes Python-Markdown#1358.

docs/change_log/index.md

@@ -6,6 +6,7 @@ Python-Markdown Change Log
 *under development*: version 3.4.4 (a bug-fix release).
 
 * Add a special case for initial 's to smarty extension (#1305).
+* Unescape any backslash escaped inline raw HTML (#1358).
 
 March 23, 2023: version 3.4.3 (a bug-fix release).
 

markdown/inlinepatterns.py

@@ -416,7 +416,7 @@ def handleMatch(self, m, data):  # pragma: no cover
 class HtmlInlineProcessor(InlineProcessor):
     """ Store raw inline html and return a placeholder. """
     def handleMatch(self, m, data):
-        rawhtml = self.unescape(m.group(1))
+        rawhtml = self.backslash_unescape(self.unescape(m.group(1)))
         place_holder = self.md.htmlStash.store(rawhtml)
         return place_holder, m.start(0), m.end(0)
 
@@ -438,6 +438,18 @@ def get_stash(m):
 
         return util.INLINE_PLACEHOLDER_RE.sub(get_stash, text)
 
+    def backslash_unescape(self, text):
+        """ Return text with backslash escapes undone (backslashes are restored). """
+        try:
+            RE = self.md.treeprocessors['unescape'].RE
+        except KeyError:  # pragma: no cover
+            return text
+
+        def _unescape(m):
+            return chr(int(m.group(1)))
+
+        return RE.sub(_unescape, text)
+
 
 class AsteriskProcessor(InlineProcessor):
     """Emphasis processor for handling strong and em matches inside asterisks."""

tests/test_syntax/inline/test_raw_html.py

@@ -28,3 +28,6 @@ def test_inline_html_angle_brackets(self):
         self.assertMarkdownRenders("<span>e>c</span>", "<p><span>e&gt;c</span></p>")
         self.assertMarkdownRenders("<span>e < c</span>", "<p><span>e &lt; c</span></p>")
         self.assertMarkdownRenders("<span>e > c</span>", "<p><span>e &gt; c</span></p>")
+
+    def test_inline_html_backslashes(self):
+        self.assertMarkdownRenders('<img src="..\\..\\foo.png">', '<p><img src="..\\..\\foo.png"></p>')