1 files changed, 49 insertions, 0 deletions
diff --git a/markdown/extensions/legacy_em.py b/markdown/extensions/legacy_em.py
new file mode 100644
index 0000000..360988b
--- /dev/null
+++ b/markdown/extensions/legacy_em.py
@@ -0,0 +1,49 @@
+'''
+Legacy Em Extension for Python-Markdown
+=======================================
+
+This extension provides legacy behavior for _connected_words_.
+
+Copyright 2015-2018 The Python Markdown Project
+
+License: [BSD](https://opensource.org/licenses/bsd-license.php)
+
+'''
+
+from . import Extension
+from ..inlinepatterns import UnderscoreProcessor, EmStrongItem, EM_STRONG2_RE, STRONG_EM2_RE
+import re
+
+# _emphasis_
+EMPHASIS_RE = r'(_)([^_]+)\1'
+
+# __strong__
+STRONG_RE = r'(_{2})(.+?)\1'
+
+# __strong_em___
+STRONG_EM_RE = r'(_)\1(?!\1)([^_]+?)\1(?!\1)(.+?)\1{3}'
+
+
+class LegacyUnderscoreProcessor(UnderscoreProcessor):
+    """Emphasis processor for handling strong and em matches inside underscores."""
+
+    PATTERNS = [
+        EmStrongItem(re.compile(EM_STRONG2_RE, re.DOTALL | re.UNICODE), 'double', 'strong,em'),
+        EmStrongItem(re.compile(STRONG_EM2_RE, re.DOTALL | re.UNICODE), 'double', 'em,strong'),
+        EmStrongItem(re.compile(STRONG_EM_RE, re.DOTALL | re.UNICODE), 'double2', 'strong,em'),
+        EmStrongItem(re.compile(STRONG_RE, re.DOTALL | re.UNICODE), 'single', 'strong'),
+        EmStrongItem(re.compile(EMPHASIS_RE, re.DOTALL | re.UNICODE), 'single', 'em')
+    ]
+
+
+class LegacyEmExtension(Extension):
+    """ Add legacy_em extension to Markdown class."""
+
+    def extendMarkdown(self, md):
+        """ Modify inline patterns. """
+        md.inlinePatterns.register(LegacyUnderscoreProcessor(r'_'), 'em_strong2', 50)
+
+
+def makeExtension(**kwargs):  # pragma: no cover
+    """ Return an instance of the LegacyEmExtension """
+    return LegacyEmExtension(**kwargs)