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

@function vertical_align($value)
  @if $value == "baseline" or $value == "top" or $value == "middle" or $value == "bottom" or $value == "text-top" or $value == "text-bottom" or $value == "super" or $value == "sub" or $value == "sub"
    @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 list_style_type($value)
  @if $value == "disc" or $value == "circle" or $value == "square" or $value == "lower-roman" or $value == "upper-roman" or $value == "lower-greek" or $value == "decimal" or $value == "decimal-leading-zero" or $value == "lower-latin" or $value == "lower-alpha" or $value == "upper-latin" or $value == "upper-alpha" or $value == "cjk-ideographic" or $value == "hiragana" or $value == "katakana" or $value == "hiragana-iroha" or $value == "katakana-iroha" or $value == "hebrew" or $value == "armenian" or $value == "georgian"
    @return true
  @else
    @return null

@function list_style_position($value)
  @if $value == "outside" or $value == "inside"
    @return true
  @else
    @return null

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