.after-hyphen {
  // We want to treat interpolation as though it's a valid identifier character,
  // which means that if it comes after a hyphen or double-hyphen it should be
  // treated as part of an interpolated identifier that includes that hyphen.
  standalone-single: -#{foo};
  standalone-double: --#{foo};

  // It also means that we shouldn't treat the hyphen as a subtraction
  // operation.
  adjacent-single: #{foo} -#{bar};
  adjacent-double: #{foo} --#{bar};
}