---input---
f'''{x
+1}'''

---tokens---
'f'           Literal.String.Affix
"'''"         Literal.String.Single
'{'           Literal.String.Interpol
'x'           Name
'\n'          Text.Whitespace

'+'           Operator
'1'           Literal.Number.Integer
'}'           Literal.String.Interpol
"'''"         Literal.String.Single
'\n'          Text.Whitespace