
doc:   [
    DocGroup({"tag": "bullet"}, [
        DocGroup({"tag": "h2"}, [
            DocChars("123"),
        ])
    ]),
]

a_del: [
    DelWithGroup([
        DelGroup([
            DelSkip(2),
            DelChars(1),
        ])
    ]),
]
a_add: [
    AddWithGroup([
        AddGroup({"tag": "p"}, [
            AddSkip(2),
        ])
    ]),
]

b_del: [
    DelGroup([
        DelSkip(1),
    ])
]
b_add: [
]
