code: function constructMetaParams(flags) {
          if (!flags || !(flags instanceof Array)) {
              flags = [ false, false, false, false ];
          }
          // Predicate to filter meta keys by
          var isActive   = function(m) { return m[1] === true; };
          // Extractor
          var extractKey = function(m) { return m[0]; };
          // Determine which meta keys were active, and map those to instances of Key
          return zipmap(Key.metaKeys, flags).filter(isActive).map(extractKey);
      }
docs: This function is reused across a number of Combo functions to
  determine the meta Key instances to construct a new Combo instance
  with.
  
  @param  {array} flags - These flags, when present, must be in CTRL > ALT > SHIFT > META order.
  @return {array} An array of Key instances matching the meta key flags passed in