text: define(['annotate', 'is-js'], function(annotate, is) {
      function flatten(a) {
          var ret = [];
  
          a.forEach(function(k) {
              if(is.array(k)) {
                  k.forEach(function(k2) {
                      ret.push(k2);
                  });
              }
              else {
                  ret.push(k);
              }
          });
  
          return ret;
      }
  
      return annotate('flatten', 'Flattens an array of arrays to a single array')
          .on(is.array, flatten);
  });
  