
doc:   [
    DocGroup({"tag": "pre"}, [
        DocGroup({"tag": "caret", "client": "c"}, []),
        DocChars("h"),
        DocGroup({"tag": "caret", "client": "d"}, [])
    ]),
]

a_del: [
    DelWithGroup([
        DelGroup([])
    ]),
]
a_add: [
    AddWithGroup([
        AddSkip(1)
    ]),
]

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