@function border-color($value)
  @if optional_color_list($value)
    @return true
  @else
    @return null

@function border-width($value)
  @if number($value)
    @return true
  @else if $value == 'thin' or $value == 'medium' or $value == 'thick'
    @return true
  @else if list($value)
    @each $assign in $value
      @if $assign == 'thin' or $assign == 'medium' or $assign == 'thick'
        @return true
      @else if number($assign)
        @return true
      @else
        @return null
  @else
    @return null

@function border-style($value)
  @if $value == 'none' or $value == 'hidden' or $value == 'solid' or $value == 'double' or $value == 'groove' or $value == 'ridge' or $value == 'inset' or $value == 'outset' or $value == 'dashed' or $value == 'dotted'
    @return true
  @else if list($value)
    @each $assign in $value
      @if $value == 'none' or $value == 'hidden' or $value == 'solid' or $value == 'double' or $value == 'groove' or $value == 'ridge' or $value == 'inset' or $value == 'outset' or $value == 'dashed' or $value == 'dotted'
        @return true
      @else
        @return null
  @else
    @return null

@function border-position($value)
  @if $value == "top" or $value == "bottom" or $value == "left" or $value == "right" or $value == "all" or $value == "horizontal" or $value == "vertical"
    @return true
  @else if list($value)
    @each $assign in $value
      @if $value == "top" or $value == "bottom" or $value == "left" or $value == "right" or $value == "all" or $value == "horizontal" or $value == "vertical"
        @return true
      @else
        @return null
  @else
    @return null
