code: function _matchAnyField(fields, matchAnyRegex) {
          var regExp = regExps ? matchAnyRegex ? regExps.any : regExps.all : null;
          if (regExp) {
              var orBuilder = parentBuilder.either();
              for (var i = 0; i < fields.length; ++i) {
                  orBuilder = orBuilder.or().field(fields[i]).is("$regex", regExp);
              }
          }
          return parentBuilder;
      }
docs: Matches the given Regular expression with at least one
  of the fields.
  @param {Array.<string>} fields Array of document fields.
  @param {boolean} [matchAnyRegex=false] If true, match any
  of the search query tokens, else match all.
  @returns {QueryBuilder} the parent Builder.
  @private