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

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