Thanks for your pull request. It looks like this may be your first contribution to a Google open source project. Before we can look at your pull request, you'll need to sign a Contributor License Agreement (CLA).

📝 Please visit https://cla.developers.google.com/ to sign.

Once you've signed, please reply here (e.g. I signed it!) and we'll verify. Thanks.

• If you've already signed a CLA, it's possible we don't have your GitHub username or you're using a different email address. Check your existing CLA data and verify that your email is set on your git commits.
• If your company signed a CLA, they designated a Point of Contact who decides which employees are authorized to participate. You may need to contact the Point of Contact for your company and ask to be added to the group of authorized contributors. If you don't know who your Point of Contact is, direct the project maintainer to go/cla#troubleshoot.
• In order to pass this check, please resolve this problem and have the pull request author add another comment and the bot will run again.

I signed it!

CLAs look good, thanks!

Does XMLSerializer API have any restrictions to not use it instead?

See also: #406 (comment)

Thanks so much! This has been my first time interacting with an open source library and it's been really great being supported.

@vsemozhetbyt Oh, I'm not aware of any! I could give that a try for just the doctype, simplifying the logic a bit. I wanted to avoid using it for the full document as it then became an XML document (which can be pretty different from what was originally intended). I'll update the PR to serialize the doctype.

You're very welcome! Thank you for the review!