Generated by SassMeister.com.

SassMeister-input.scss

// ----
// Sass (v3.4.12)
// Compass (v1.0.3)
// ----

$__property-append-map__: () !global;

@mixin \+($property, $value: null) {
  $selector: selector-parse(&);
  @if not map-has-key($__property-append-map__, $selector) {
    $__property-append-map__: map-merge($__property-append-map__, ($selector: ())) !global;
  }
  
  $selector-property: get(get($__property-append-map__, $selector), $property);
  @if $property == null {
    $__property-append-map__: map-merge($__property-append-map__, ($selector: ($property: ($value,))))
  }
  
  $property-list: map-get($__property-append-map__, $selector);
  $__property-append-map__: map-merge($__property-append-map__, ($selector: append($property-list, unquote($value), comma))) !global;
}

@function \+($property) {
  $property-list: map-get($__property-append-map__, selector-parse(&));
  @return $property-list;
}

.foo {
  @include \+(animation-name, foo-active-1);
  @include \+(animation-name, foo-active-2);
  
  animation-name: \+(animation-name);
}

.bar {
  @include \+(transition-property, opacity);
  @include \+(transition-property, transform);
  
  transition-property: \+(transition-property);
}

SassMeister-output.css

(((.foo,)): ()) isn't a valid CSS value.