---input---
f'result: {value:{width}.{precision}}'

---tokens---
'f'           Literal.String.Affix
"'"           Literal.String.Single
'result: '    Literal.String.Single
'{'           Literal.String.Interpol
'value'       Name
':'           Literal.String.Interpol
'{'           Literal.String.Interpol
'width'       Name
'}'           Literal.String.Interpol
'.'           Literal.String.Single
'{'           Literal.String.Interpol
'precision'   Name
'}'           Literal.String.Interpol
'}'           Literal.String.Interpol
"'"           Literal.String.Single
'\n'          Text.Whitespace