Clarify enum variant NovelLinePart and expand doc comments #3227

Job	Run time
Actionlint	1m 14s
Test x86_64-unknown-linux-gnu	4m 26s
Test x86_64-apple-darwin	5m 35s
Test x86_64-pc-windows-msvc	5m 18s
Rustfmt	1m 26s
Test aarch64-unknown-linux-gnu	6m 0s
Test aarch64-apple-darwin	3m 45s
Check Linux Packaging	4m 32s
Test x86_64-unknown-linux-musl	4m 40s
Output Regression Test	4m 49s
Test Linux (latest stable Rust)	2m 14s
Test with MIME database	4m 6s
	48m 5s

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