MetaLayer is a concept introduced by Daniel Einspanjer that allows:
Metalayers are simply javascript files that live in the solution folder. They can be imported from the template files using the following command:
<script type="text/javascript" src="../solution:path:MyMetaLayer.js"></script>
More than one file can be included. Using this method, a developer can leave only html design in the template.html file and put all the components definition in the MetaLayers.
This same method can be used to include other types of files from the solution directory, like images, css resources, etc.