@function kf-stretch($multiplier-or-duration, $animation-map) {
  $animation-map: _normalize-map-hierarchy($animation-map, tepv);

  $multiplier: 1;
  $unit: unit($multiplier-or-duration);
  $current-duration: _calculate_animation_length($animation-map);
  @if $unit == "" {
    $multiplier: $multiplier-or-duration;
  } @else if $unit == "ms" or $unit == "s" {
    $multiplier: $multiplier-or-duration / $current-duration;
  } @else {
    @warn Cannot use kf-stretch on unit '#{$unit}';
  }
  $new-total-duration: $current-duration * $multiplier;

  $seperated: _kf-properties-extractor($animation-map);
  $anim-map: nth($seperated, 1);
  $prop-map: nth($seperated, 2);

  $return-map: ();
  @each $t, $epv in $anim-map {
    $return-map: map-merge($return-map, (($t * $multiplier): $epv));
  }

  $prop-map: map-merge($prop-map, (_kf-duration: $new-total-duration));
  @return map-merge(
    $return-map,
    $prop-map
  );
}

@mixin kf-stretch($m...) {
  @include kf(kf-stretch($m...));
}