---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.Single
'x'           Literal.String.Single
"'"           Literal.String.Single
']'           Punctuation
'}'           Literal.String.Interpol
' def'        Literal.String.Double
'"'           Literal.String.Double
'\n'          Text.Whitespace