doc:   [
    DocGroup({"tag": "h1"}, [
        DocGroup({"client": "left", "tag": "caret"}, []),
        DocGroup({"tag": "caret", "client": "right"}, []),
        DocChars("Hello world!")
    ]),
    DocGroup({"tag": "p"}, [
        DocChars("What\'s up with you?")
    ])
]

a_del: [
    DelGroup([
        DelGroup([]),
        DelSkip(13)
    ])
]
a_add: [
    AddGroup({"tag": "h1"}, [
        AddChars("c  c11j"), AddGroup({"tag": "caret", "client": "left"}, []),
        AddChars("820h"), AddSkip(13)
    ])
]

b_del: [
    DelGroup([
        DelWithGroup([]),
        DelGroup([]),
        DelSkip(12)
    ]),
    DelSkip(1)
]
b_add: [
    AddGroup({"tag": "h1"}, [
        AddChars("fn7g017824"), AddWithGroup([]),
        AddChars("V "), AddSkip(12)
    ]),
    AddWithGroup([
        AddGroup({"client": "right", "tag": "caret"}, [])
    ])
]