This is a para.
[id]: http://www.example.com/

[otherid1]: http://wwww.example.com/ "title 1"
[otherid2]: http://wwww.example.com/ 'title 2'
[otherid3]: <some spaces.html>
[otherid4]: <some spaces.html> 'title'
[otherid5]: some spaces.html
[otherid6]: some spaces.html 'title'
[otherid7]: some spaces
            "title"

[break]:	http://www.example.com/test/asdf.html
                'Another title'

[1]: ignored.url
 [1]: one.url
  [2]: two.url
   [3]: three.url
    [4]: nourl

Points to [1] and [2] and [3] but not [4]

[_.:,;!?-]: http://example.com

Points to [_.:,;!?-]