doc:   [
    DocGroup({"tag": "h1"}, [
        DocChars("1234")
    ]),
    DocGroup({"tag": "bullet"}, [
        DocGroup({"tag": "h1"}, [
            DocChars("1234")
        ])
    ])
]

a_del: [
    DelSkip(1),
    DelGroup([
        DelGroup([
            DelSkip(4)
        ])
    ])
]
a_add: [
    AddGroup({"tag": "bullet"}, [
        AddSkip(1),
    ]),
    AddGroup({"tag": "h1"}, [
        AddSkip(4),
    ])
]

b_del: [
    DelSkip(1),
    DelWithGroup([
        DelWithGroup([
            DelChars(1)
        ])
    ])
]
b_add: [
    AddSkip(1),
    AddWithGroup([
        AddWithGroup([
            AddChars("$"),
        ])
    ])
]