doc:   [
    DocGroup({"tag": "h2"}, [
        DocChars(" Cl43"), DocGroup({"tag": "caret", "client": "left"}, []),
        DocChars("K"), DocGroup({"client": "right", "tag": "caret"}, []),
        DocChars("e uJ r ")
    ]),
    DocGroup({"tag": "h3"}, [
        DocChars(" 7GxDE c3  SdIHello world!is0y 7QNsLhat\'s up with you?")
    ])
]

a_del: [
    DelWithGroup([
        DelSkip(4), DelChars(1), DelGroup([])
    ])
]
a_add: [
    AddWithGroup([
        AddSkip(3), AddChars("H"), AddGroup({"tag": "caret", "client": "left"}, []),
        AddSkip(1)
    ])
]

b_del: [
    DelWithGroup([
        DelSkip(4), DelChars(1), DelWithGroup([]),
        DelSkip(1), DelGroup([])
    ])
]
b_add: [
    AddWithGroup([
        AddSkip(4), AddChars("w"), AddGroup({"tag": "caret", "client": "right"}, []),
        AddWithGroup([]),
        AddSkip(1)
    ])
]