---input---
[an example][id]
[id]: http://example.com

---tokens---
'['           Text
'an example'  Name.Tag
']'           Text
'['           Text
'id'          Name.Label
']'           Text
'\n'          Text.Whitespace

'['           Text
'id'          Name.Label
']: '         Text
'http://example.com' Name.Attribute
'\n'          Text.Whitespace