Example
Properties of a multi-property component will merge if defined by multiple mixins and/or the entity. For example:
<a-scene>
<a-assets>
<a-mixin id="box" geometry="primitive: box"></a-mixin>
<a-mixin id="tall" geometry="height: 10"></a-mixin>
<a-mixin id="wide" geometry="width: 10"></a-mixin>
</a-assets>
<a-entity mixin="wide tall box" geometry="depth: 2"></a-entity>
</a-scene>
All of the geometry component properties will merge since they are included as mixins and defined on the entity. The entity would then be equivalent to:
<a-entity geometry="primitive: box; height: 10; depth: 2; width: 10"></a-entity>
