forward() {
    if (this.right === null) {
      error.unexpectedCase();
    }

    switch (this.right.content.constructor) {
      case ContentFormat:
        if (!this.right.deleted) {
          updateCurrentAttributes(this.currentAttributes,
          /** @type {ContentFormat} */
          this.right.content);
        }

        break;

      default:
        if (!this.right.deleted) {
          this.index += this.right.length;
        }

        break;
    }

    this.left = this.right;
    this.right = this.right.right;
  }
Only call this if you know that this.right is defined