---input---
f"""abc {a["x"]} def"""

---tokens---
'f'           Literal.String.Affix
'"""'         Literal.String.Double
'abc '        Literal.String.Double
'{'           Literal.String.Interpol
'a'           Name
'['           Punctuation
'"'           Literal.String.Double
'x'           Literal.String.Double
'"'           Literal.String.Double
']'           Punctuation
'}'           Literal.String.Interpol
' def'        Literal.String.Double
'"""'         Literal.String.Double
'\n'          Text
