Test HTML serialization.

Test that an `AtomicString` returned from a Pattern doesn't cause a crash.

Test Extension loading with a class instance.

Test `State.isstate()`.

Test loading of an Extension with no makeExtension function.

Test failure of an extension to load.

Test that reset call remove Meta entirely

Test document with only metadata and no newline at end.

Test document without Meta Data.

Test preservation of tag case.

Test that a nested `AtomicString` is not parsed.

Test loading a non Extension object as an extension.

Test `BlockParser.parseChunk`.

Test `BlockParser.parseDocument`.

Test serialization of `ProcessignInstruction`.

Test serialization of `QName` attribute.

Test `QName` escaping.

Test `QName` that is already partially escaped.

Test serialization of `QName` tag.