@function time($value)
  @if unit_number($value) and unit($value) == 's'
    @return ture
  @else
    @return null

@function timing_function($value)
  @if string($value)
    @if $value == 'ease' or $value == 'linear' or $value == 'ease-in' or $value == 'ease-out' or $value == 'ease-in-out' or str-slice($value, 1, 12) == 'cubic-bezier'
      @return ture
    @else
      @return null
  @else
    @return null

@function delay($value)
  @if string($value) and str-slice($value, 1, 1) == '/' and str-slice($value, -1, -1) == 's'
    @return str-slice($value, 2)
  @else
    @return null

//////////////////
// transition
//////////////////

@function transition_duration($value)
  @return time($value)

@function transition_timing_function($value)
  @return timing_function($value)

@function transition_delay($value)
  @return delay($value)

@function transition-property($value)
  @if string($value)
    @if not transition_timing_function($value) or not transition_duration($value) or not transition_delay($value)
      @return ture
    @else
      @return null
  @else if list($value)
    @return ture
  @else
    @return null

//////////////////
// animation
//////////////////

@function animation_duration($value)
  @return time($value)

@function animation_timing_function($value)
  @return timing_function($value)

@function animation_delay($value)
  @return delay($value)

@function animation_iteration_count($value)
  @if unitless_number($value) or (string($value) and $value == 'infinite')
    @return ture
  @else
    @return null

@function animation_direction($value)
  @if string($value) and ($value == 'normal' or $value == 'alternate')
    @return ture
  @else
    @return null

@function animation_fill_mode($value)
  @if string($value) and ($value == 'nonel' or $value == 'forwards' or $value == 'backwards' or $value == 'both')
    @return ture
  @else
    @return null

@function animation_play_state($value)
  @if string($value) and ($value == 'running' or $value == 'paused')
    @return ture
  @else
    @return null

@function animation_name($value)
  @if string($value)
    @if not animation_timing_function($value) or not animation_duration($value) or not animation_iteration_count($value) or not animation_direction($value) or not animation_fill_mode($value) or not animation_play_state($value)
      @return ture
    @else
      @return null
  @else
    @return null