code: function sortProducts( products ) {
  	let planItems, includedItems, domainItems, creditItems, otherItems;
  
  	planItems = products.filter( isPlan );
  
  	includedItems = products.filter( isIncludedWithPlan );
  
  	domainItems = difference( products, includedItems );
  	domainItems = domainItems.filter( isDomainProduct );
  	domainItems = toPairs( groupBy( domainItems, 'meta' ) );
  	domainItems = sortBy( domainItems, function( pair ) {
  		if ( pair[ 1 ][ 0 ] && pair[ 1 ][ 0 ].cost === 0 ) {
  			return -1;
  		}
  		return pair[ 0 ];
  	} );
  	domainItems = domainItems.map( function( pair ) {
  		return sortBy( pair[ 1 ], getDomainProductRanking );
  	} );
  	domainItems = flatten( domainItems );
  
  	creditItems = products.filter( isCredits );
  
  	otherItems = difference( products, planItems, domainItems, includedItems, creditItems );
  
  	return planItems
  		.concat( includedItems )
  		.concat( domainItems )
  		.concat( otherItems )
  		.concat( creditItems );
  }
docs: Sorts all products in the following order:
  
  1. Plan
  2. Domain Cart Items. Included in plans come first.
  a. Domain Registration
  b. Domain Mapping
  c. Privacy Protection
  3. Other Cart Items
  4. Credits Cart Item
  
  @param {Object[]} products
  
  @returns {Object[]} the sorted list of items in the shopping cart