doc:   [
    DocGroup({"tag": "p"}, [
        DocChars("12345")
    ]),
    DocGroup({"tag": "p"}, [
        DocGroup({"client": "e", "tag": "caret"}, []),
        DocChars("5")
    ]),
    DocGroup({"tag": "p"}, [
        DocChars("u"),
        DocGroup({"client": "j", "tag": "caret"}, []),
        DocChars("A")
    ]),
]

a_del: [
    DelGroup([
        DelSkip(5),
    ]),
    DelGroup([
        DelGroup([]),
        DelSkip(1)
    ])
]
a_add: [
    AddGroup({"tag": "bullet"}, [
        AddGroup({"tag": "p"}, [
            AddSkip(5),
            AddChars("123")
        ])
    ]),
    AddGroup({"tag": "p"}, [
        AddSkip(1)
    ])
]

b_del: [
    DelSkip(1),
    DelGroup([
        DelSkip(2)
    ]),
    DelGroup([
        DelChars(1),
        DelSkip(2)
    ])
]
b_add: [
    AddSkip(1),
    AddGroup({"tag": "p"}, [
        AddSkip(4)
    ])
]