Ensure md_in_html does not drop content

Fixes #1526.

Co-authored-by: Dmitry Shachnev <mitya57@users.noreply.github.com>

Author: facelessuser

docs/changelog.md

@@ -9,6 +9,12 @@ The format is based on [Keep a Changelog](https://keepachangelog.com/en/1.1.0/),
 and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0.html).
 See the [Contributing Guide](contributing.md) for details.
 
+## [Unreleased]
+
+### Fixed
+
+* Fixed dropped content in `md_in_html` (#1526).
+
 ## [3.8.0] - 2025-04-09
 
 ### Changed

markdown/extensions/md_in_html.py

@@ -387,12 +387,16 @@ def run(self, parent: etree.Element, blocks: list[str]) -> bool:
             element = self.parser.md.htmlStash.rawHtmlBlocks[index]
             if isinstance(element, etree.Element):
                 # We have a matched element. Process it.
-                blocks.pop(0)
+                block = blocks.pop(0)
                 parent.append(element)
                 self.parse_element_content(element)
                 # Cleanup stash. Replace element with empty string to avoid confusing postprocessor.
                 self.parser.md.htmlStash.rawHtmlBlocks.pop(index)
                 self.parser.md.htmlStash.rawHtmlBlocks.insert(index, '')
+                content = block[m.end(0):]
+                # Ensure the rest of the content gets handled
+                if content:
+                    blocks.insert(0, content)
                 # Confirm the match to the `blockparser`.
                 return True
         # No match found.

tests/test_syntax/extensions/test_md_in_html.py

@@ -1517,6 +1517,27 @@ def test_md1_code_cdata(self):
             extensions=['md_in_html']
         )
 
+    def test_trailing_content_after_tag_in_md_block(self):
+
+        # It should be noted that this is not the way `md_in_html` is intended to be used.
+        # What we are specifically testing is an edge case where content was previously lost.
+        # Lost content should not happen.
+        self.assertMarkdownRenders(
+            self.dedent(
+                """
+                <div markdown>
+                <div class="circle"></div>AAAAA<div class="circle"></div>
+                </div>
+                """
+            ),
+            '<div>\n'
+            '<div class="circle"></div>\n'
+            '<p>AAAAA<div class="circle"></p>\n'
+            '</div>\n'
+            '</div>',
+            extensions=['md_in_html']
+        )
+
 
 def load_tests(loader, tests, pattern):
     """ Ensure `TestHTMLBlocks` doesn't get run twice by excluding it here. """