#functions {
  @var: 10;
  color: _color("evil red"); // #660000
  width: increment(15);
  height: undefined("self");
  border-width: add(2, 3);
  variable: increment(@var);
}

#built-in {
  @r: 32;
  escaped: e("-Some::weird(#thing, y)");
  lighten: lighten(#ff0000, 40%);
  darken: darken(#ff0000, 40%);
  saturate: saturate(#29332f, 20%);
  desaturate: desaturate(#203c31, 20%);
  greyscale: greyscale(#203c31);
  spin-p: spin(hsl(340, 50%, 50%), 40);
  spin-n: spin(hsl(30, 50%, 50%), -40);
  format: %("rgb(%d, %d, %d)", @r, 128, 64);
  format-string: %("hello %s", "world");
  format-multiple: %("hello %s %d", "earth", 2);
  format-url-encode: %('red is %A', #ff0000);
  eformat: e(%("rgb(%d, %d, %d)", @r, 128, 64));

  hue: hue(hsl(98, 12%, 95%));
  saturation: saturation(hsl(98, 12%, 95%));
  lightness: lightness(hsl(98, 12%, 95%));
  rounded: round(@r/3);
  roundedpx: round(10px / 3);
  percentage: percentage(10px / 50);
  color: color("#ff0011");

  .is-a {
    color: iscolor(#ddd);
    color: iscolor(red);
    color: iscolor(rgb(0, 0, 0));
    keyword: iskeyword(hello);
    number: isnumber(32);
    string: isstring("hello");
    pixel: ispixel(32px);
    percent: ispercentage(32%);
    em: isem(32em);
  }
}

#alpha {
  alpha: darken(hsla(25, 50%, 50%, 0.6), 10%);
}
