@function display($value)
  @if $value == "inline" or $value == "block" or $value == "list-item" or $value == "run-in" or $value == "inline-block" or $value == "table" or $value == "inline-table" or $value == "table-row-group" or $value == "table-header-group" or $value == "table-footer-group" or $value == "table-row" or $value == "table-column-group" or $value == "table-column" or $value == "table-cell" or $value == "table-caption" or $value == "none" or $value == "flex" or $value == "inline-flex"
    @return true
  @else
    @return null

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

@function color($value)
  @if type-of($value) == color
    @return true
  @else
    @return null

@function font_weight($value)
  @if $value == "bold" or $value == "normal"
    @return true
  @else if unitless_number($value)
    @if $value >= 100
      @return true
    @else
      @return null
  @else
    @return null

@function font_style($value)
  @if $value == "normal" or $value == "italic" or $value == "oblique"
    @return true
  @else
    @return null

@function white_space($value)
  @if $value == "normal" or $value == "pre" or $value == "nowrap"
    @return true
  @else
    @return null

@function text_decoration($value)
  @if $value == "none" or $value == "underline" or $value == "overline" or $value == "line-through" or $value == "blink"
    @return true
  @else
    @return null
