code: function prefixCompositionIds( composition, containerItem ) {
        const prefixedAreas = {};
        const itemIds = {};
        forEachArea( composition, items => {
           items.forEach( item => {
              if( has( item, 'id' ) ) {
                 item.id = itemIds[ item.id ] = containerItem.id + ID_SEPARATOR + item.id;
              }
           } );
        } );
  
        forEachArea( composition, (items, areaName) => {
           const index = areaName.indexOf( '.' );
           const itemId = index > 0 ? areaName.substr( 0, index ) : null;
           const areaSuffix = index > 0 ? areaName.substr( index ) : null;
  
           // All areas prefixed with a local widget id need to be prefixed as well
           const prefixedName = ( itemId && itemId in itemIds ) ?
              itemIds[ itemId ] + areaSuffix :
              areaName;
  
           prefixedAreas[ prefixedName ] = items;
        } );
        composition.definition.areas = prefixedAreas;
        return composition;
     }
docs: /////////////////////////////////////////////////////////////////////////////////////////////////////////