<===> input.scss
// The CSS nav-up property and its siblings allow ID tokens in their values, so
// Sass parses any tokens that start with a "#" followed by an identifier as an
// ID if it can't be parsed as a color.
a {
  // These IDs are the wrong number of letters to be a hex color.
  two-letters: #ab;
  five-letters: #abcde;
  seven-letters: #abcdefa;
  nine-letters: #abcdefabc;

  // These IDs contain letters outside the hexadecimal gamut.
  three-letters-not-hex: #axc;
  four-letters-not-hex: #axcd;
  six-letters-not-hex: #abcxde;
  eight-letters-not-hex: #abcxdefa;
}

<===> output.css
a {
  two-letters: #ab;
  five-letters: #abcde;
  seven-letters: #abcdefa;
  nine-letters: #abcdefabc;
  three-letters-not-hex: #axc;
  four-letters-not-hex: #axcd;
  six-letters-not-hex: #abcxde;
  eight-letters-not-hex: #abcxdefa;
}