code: function hsl(hue, saturation, lightness){
    if (1 == arguments.length) {
      utils.assertColor(hue, 'color');
      return hue.hsla;
    } else {
      return hsla(
          hue
        , saturation
        , lightness
        , new nodes.Unit(1));
    }
  }
docs: Convert the given `color` to an `HSLA` node,
  or h,s,l component values.
  
  Examples:
  
  hsl(10, 50, 30)
  // => HSLA
  
  hsl(#ffcc00)
  // => HSLA
  
  @param {Unit|HSLA|RGBA} hue
  @param {Unit} saturation
  @param {Unit} lightness
  @return {HSLA}
  @api public