docs: function(key, regex, modifiers) {
          this._addCondition(key, '$regex', regex);
          if (!modifiers) {
            modifiers = '';
          }
          // Javascript regex options support mig as inline options but store them
          // as properties of the object. We support mi & should migrate them to
          // modifiers
          if (regex.ignoreCase) {
            modifiers += 'i';
          }
          if (regex.multiline) {
            modifiers += 'm';
          }
  
          if (modifiers && modifiers.length) {
            this._addCondition(key, '$options', modifiers);
          }
          return this;
        }