@function position($value)
  @if $value == "top" or $value == "bottom" or $value == "left" or $value == "right" or $value == "center"
    @return true
  @else
    @return null

@function direction($value)
  @if string($value)
    @if $value == "top" or $value == "bottom" or $value == "left" or $value == "right" or $value == "horizontal" or $value == "vertical" or $value == "all"
      @return true
    @else
      @return null
  @else
    @return null

@function four_position($value)
  @if $value == "top" or $value == "bottom" or $value == "left" or $value == "right"
    @return true
  @else
    @return null

@function top($value)
  @if $value == "top"
    @return true
  @else
    @return null

@function bottom($value)
  @if $value == "bottom"
    @return true
  @else
    @return null

@function left($value)
  @if $value == "left"
    @return true
  @else
    @return null

@function right($value)
  @if $value == "right"
    @return true
  @else
    @return null

@function center($value)
  @if $value == "center"
    @return true
  @else
    @return null

@function position_vertical($value)
  @if $value == 'bottom' or $value == 'top'
    @return true
  @else
    @return null

@function position_horizontal($value)
  @if $value == 'left' or $value == 'right'
    @return true
  @else
    @return null

@function all($value)
  @if $value == "all"
    @return true
  @else
    @return null

@function horizontal($value)
  @if $value == "horizontal"
    @return true
  @else
    @return null

@function vertical($value)
  @if $value == "vertical"
    @return true
  @else
    @return null