txt.gsub!(/<sub>(.*?)<\/sub>/, '_{\1}')
txt.gsub!(/(^|_)\{(.)\}/, '\1\2')
+ # List items are converted to *). We don't have special support for
+ # nested or ordered lists.
+ txt.gsub!(/<li>/, ' *) ')
+
# All other tags are just removed
txt.gsub!(/<[^>]+>/, '')