append 
 Adds the given value to the end of the given array
   Arguments 
  array - The array to add to  element... - The elements to add  
   Example 
 {
  "$template": {
	"$comment": "The field below will be [1, 2, 3, 5, 8, 10, 12]",
	"test": "{{[1, 2, 3, 5, 8, 10].append(12)}}"
  }
}