4 files changed, 78 insertions, 1 deletions
diff --git a/docs/extensions/Smart_Strong.txt b/docs/extensions/Smart_Strong.txt
new file mode 100644
index 0000000..c939016
--- /dev/null
+++ b/docs/extensions/Smart_Strong.txt
@@ -0,0 +1,30 @@
+Smart_Strong
+------------
+
+Summary
+
+The Markdown Smart_Strong Extension adds smarter handling of double underscores
+within words. This does for double underscores what 'smart_emphasis' does for 
+single underscores.
+
+The Smart_Strong Extension is included in the standard Markdown library.
+
+Usage
+-----
+
+    >>> import markdown
+    >>> markdown.markdown('Text with double__underscore__words.', \
+                          extensions=['smart_strong'])
+    u'<p>Text with double__underscore__words.</p>'
+    >>> markdown.markdown('__Strong__ still works.', \
+                          extensions=['smart_strong'])
+    u'<p><strong>Strong</strong> still works.</p>'
+    >>> markdown.markdown('__this__works__too__.', \
+                          extensions=['smart_strong'])
+    u'<p><strong>this__works__too</strong>.</p>'
+
+This extension is also included with the [[Extra]] Extension. You may call that
+extension to get this behavior with all the other features of 'Extra'.
+
+    >>> markdown.markdown(text, extensions=['extra'])
+
diff --git a/docs/extensions/extra.txt b/docs/extensions/extra.txt
index 817d58f..018a849 100644
--- a/docs/extensions/extra.txt
+++ b/docs/extensions/extra.txt
@@ -15,6 +15,7 @@ The supported extensions include:
 * [[Footnotes]]
 * [[HeaderId]]
 * [[Tables]]
+* [[Smart_Strong]]
 
 See each individual extension for syntax documentation. Extra and all it's 
 supported extensions are included in the standard Markdown library.
diff --git a/markdown/extensions/extra.py b/markdown/extensions/extra.py
index e569029..60ad55e 100644
--- a/markdown/extensions/extra.py
+++ b/markdown/extensions/extra.py
@@ -29,7 +29,8 @@ when you upgrade to any future version of Python-Markdown.
 
 import markdown
 
-extensions = ['fenced_code',
+extensions = ['smart_strong',
+              'fenced_code',
               'footnotes',
               'headerid',
               'def_list',
diff --git a/markdown/extensions/smart_strong.py b/markdown/extensions/smart_strong.py
new file mode 100644
index 0000000..4fb3280
--- /dev/null
+++ b/markdown/extensions/smart_strong.py
@@ -0,0 +1,45 @@
+'''
+Smart_Strong Extension for Python-Markdown
+==========================================
+
+This extention as a smarter handleing of double underscores within words.
+
+Simple Usage:
+
+    >>> import markdown
+    >>> markdown.markdown('Text with double__underscore__words.', \
+                          extensions=['smart_strong'])
+    u'<p>Text with double__underscore__words.</p>'
+    >>> markdown.markdown('__Strong__ still works.', \
+                          extensions=['smart_strong'])
+    u'<p><strong>Strong</strong> still works.</p>'
+    >>> markdown.markdown('__this__works__too__.', \
+                          extensions=['smart_strong'])
+    u'<p><strong>this__works__too</strong>.</p>'
+
+Copyright 2011
+[Waylan Limberg](http://achinghead.com)
+
+'''
+
+import re
+import markdown
+from markdown.inlinepatterns import SimpleTagPattern
+
+SMART_STRONG_RE = r'(?<!\w)(_{2})(?!_)(.+?)(?<!_)\2(?!\w)'
+STRONG_RE = r'(\*{2})(.+?)\2'
+
+class SmartEmphasisExtension(markdown.extensions.Extension):
+    """ Add smart_emphasis extension to Markdown class."""
+
+    def extendMarkdown(self, md, md_globals):
+        """ Modify inline patterns. """
+        md.inlinePatterns['strong'] = SimpleTagPattern(STRONG_RE, 'strong')
+        md.inlinePatterns['strong2'] = SimpleTagPattern(SMART_STRONG_RE, 'strong')
+
+def makeExtension(configs={}):
+    return SmartEmphasisExtension(configs=dict(configs))
+
+if __name__ == '__main__':
+    import doctest
+    doctest.testmod()