docs: function(arrayA, arrayB) {
  
      var returnArray =[];
      var i = 0;
      arrayA.forEach(function(doc){
          if (common.isUseless(theIDCheck(arrayB, doc) )) { i += 1; }
          else {
              i += 1;
              returnArray.push([doc, theIDCheck(arrayB, doc)]); ////push a pair of matching docs
          };
      });
  
      if ( (i == arrayA.length) && ( common.isUseless(returnArray[0]) ) ) {    return null;    }
      else if ( (i == arrayA.length) && (common.isUseless(returnArray[0]) == false ) ) {    return returnArray;    };
  }