code: function BSONRegExp(pattern, options) {
    if (!(this instanceof BSONRegExp)) return new BSONRegExp();
  
    // Execute
    this._bsontype = 'BSONRegExp';
    this.pattern = pattern || '';
    this.options = options || '';
  
    // Validate options
    for (var i = 0; i < this.options.length; i++) {
      if (
        !(
          this.options[i] === 'i' ||
          this.options[i] === 'm' ||
          this.options[i] === 'x' ||
          this.options[i] === 'l' ||
          this.options[i] === 's' ||
          this.options[i] === 'u'
        )
      ) {
        throw new Error('the regular expression options [' + this.options[i] + '] is not supported');
      }
    }
  }
docs: A class representation of the BSON RegExp type.
  
  @class
  @return {BSONRegExp} A MinKey instance