resolves #59 track header attributes in source document and assign to… #722

Job	Run time
activate	1s
build (ubuntu-latest, jruby-9.3)	1m 11s
build (ubuntu-latest, 2.7)	22s
build (windows-latest, jruby-9.3)	2m 24s
build (windows-latest, 2.7)	3m 31s
build (windows-latest, 3.3)	2m 41s
build (ubuntu-latest, jruby-9.2)	1m 10s
build (ubuntu-latest, truffleruby)	34s
build (macos-latest, 3.3)	12s
build (ubuntu-latest, 3.3, 2.0.15)	12s
build (ubuntu-latest, 3.3, primary)	14s
	12m 32s

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