out of order sections causing issues

When there are sections defined out of order, it seems tomlkit does not like it. Original issue was reported at https://github.com/python-poetry/poetry/issues/4718.

The following code runs without issues, however does not modify the toml. Using content.value_insert_after() causes AttributeError: 'dict' object has no attribute '_insert_after'.

If we remove build-system from the toml, the code below raises AttributeError: 'Table' object has no attribute '_insert_after'. However using content.value succeeds with the right results.

import tomlkit


TOML = tomlkit.parse("""\
[tool.poetry]
name = "foobar"
version = "0.1.0"
description = ""
readme = "README.md"

[tool.poetry.dependencies]
python = "^3.10"

[build-system]
requires = ["poetry-core"]
build-backend = "poetry.core.masonry.api"

[tool.poetry.plugins]
""")


if __name__ == '__main__':
    content = TOML["tool"]["poetry"]
    content._insert_after("dependencies", "group", tomlkit.table(is_super_table=True))
    content["group"]["one"] = tomlkit.table(is_super_table=True)
    content["group"]["one"]["dependencies"] = tomlkit.table()
    print(TOML.as_string())

Start with the reproducer.py code in the issue and run it against the shown TOML, comparing _insert_after, value_insert_after(), and content.value. Trace how out-of-order sections and the build-system table are represented; done means inserting the group section produces the intended TOML without either AttributeError.