code: function(revision)
    {
      if ( isFunction( revision ) )
      {
        this.revisionFunction = revision;
      }
      else if ( isString( revision ) )
      {
        this.revisionFunction = function(a, b)
        {
          var ar = isObject( a ) && revision in a ? a[ revision ] : undefined;
          var br = isObject( b ) && revision in b ? b[ revision ] : undefined;
  
          return ar === undefined || br === undefined ? false : compare( ar, br ) > 0;
        };
      }
      else
      {
        this.revisionFunction = function(a, b)
        {
          return false;
        };
      }
    }
docs: Sets a revision comparision function for this database. It can be a field name or a function. This is used to avoid updating model data that is older than the model's current data.