  #should NOT be included0 as a chapter

  # should be included0 as a chapter

 #should NOT be included1 as a chapter

 # should be included1 as a chapter

#should NOT be included2 as a chapter

# should be included2 as a chapter

These input is taken from Yinzuo Jiang (@jiangyinzuo)'s
commit in #3747.


   #not-title-1


   # title 1
 ## title 2
   # title 3
 ### title 4
 #### title 5
 ##### title 6
 ###### title 7

xxx# not title 2
xxx## not title 3
xxx### not title 4
xxx#### not title 5
	# not title 6 when starting with tab

..##### not title 7
 ####### not title 8
