---input---
This example is unbalanced open-close.
We can't treat these easily.

{+ added? -]
[- deleted? +}

suddenly closed -]
suddenly closed +}

{+ added? [- deleted?

---tokens---
'This example is unbalanced open' Text
'-'           Text
"close.\nWe can't treat these easily.\n\n" Text

'{+'          Generic.Inserted
' added? '    Generic.Inserted
'-]'          Generic.Inserted
'\n'          Text

'[-'          Generic.Deleted
' deleted? '  Generic.Deleted
'+}'          Generic.Deleted
'\n\nsuddenly closed ' Text
'-'           Text
']'           Text
'\nsuddenly closed ' Text
'+'           Text
'}'           Text
'\n\n'        Text

'{+'          Generic.Inserted
' added? '    Generic.Inserted
'[-'          Generic.Inserted
' deleted?\n' Generic.Inserted