@function background_color($value)
  @if color($value)
    @return true
  @else
    @return null

@function background_position($value)
  @if list($value)
    @if string(nth($value, 1)) and not str-index(nth($value, 1), '/')
      @return true
    @else if string(nth($value, 1)) and not str-index(nth($value, 1), '\/')
      @return true
    @else if number(nth($value, 1))
      @return true
    @else
      @return null
  @else
    @return null

@function background_size($value)
  @if $value == auto or $value == contain or $value == cover
    @return true
  @else if list($value)
    @if string(nth($value, 1)) and str-index(nth($value, 1), '\/')
      @return ture
    @else if string(nth($value, 1)) and str-index(nth($value, 1), '/')
      @return ture
    @else
      @return null
  @else
    @return null

@function background_size_value($value)
  @if background_size($value)
    @if list($value)
      @if string(nth($value, 1)) and str-index(nth($value, 1), '\/')
        @return unquote(string-replace(nth($value, 1), '\\/', '/') + ' ' + nth($value, 2))
      @else
        @return unquote('/' + $value)
    @else
      @return  unquote('/' + $value)
  @else
    @return null

@function background_repeat($value)
  @if $value == no-repeat or $value == repeat or $value == repeat-x or $value == repeat-y
    @return true
  @else
    @return null

@function background_attachment($value)
  @if $value == fixed or $value == scroll
    @return true
  @else
    @return null

@function background_image($value)
  @if image($value)
    @return true
  @else
    @return null

@function background_gradient($value)
  @if string($value)
    @if str-index($value, linear-gradient) or str-index($value, radial-gradient) or str-index($value, repeating-)
      @return true
    @else
      @return null
  @else
    @return null

@function background_clip($value)
  @if $value == \"border" or $value == \"padding" or $value == \"content" or $value == \"text"
    @return true
  @else
    @return null