def __init_subclass__(cls, **kwargs: Unpack[ConfigDict]):
            """This signature is included purely to help type-checkers check arguments to class declaration, which
            provides a way to conveniently set model_config key/value pairs.

            ```python
            from pydantic import BaseModel

            class MyModel(BaseModel, extra='allow'): ...
            ```

            However, this may be deceiving, since the _actual_ calls to `__init_subclass__` will not receive any
            of the config arguments, and will only receive any keyword arguments passed during class initialization
            that are _not_ expected keys in ConfigDict. (This is due to the way `ModelMetaclass.__new__` works.)

            Args:
                **kwargs: Keyword arguments passed to the class definition, which set model_config

            Note:
                You may want to override `__pydantic_init_subclass__` instead, which behaves similarly but is called
                *after* the class is fully initialized.
            """
This signature is included purely to help type-checkers check arguments to class declaration, which
            provides a way to conveniently set model_config key/value pairs.

            ```python
            from pydantic import BaseModel

            class MyModel(BaseModel, extra='allow'): ...
            ```

            However, this may be deceiving, since the _actual_ calls to `__init_subclass__` will not receive any
            of the config arguments, and will only receive any keyword arguments passed during class initialization
            that are _not_ expected keys in ConfigDict. (This is due to the way `ModelMetaclass.__new__` works.)

            Args:
                **kwargs: Keyword arguments passed to the class definition, which set model_config

            Note:
                You may want to override `__pydantic_init_subclass__` instead, which behaves similarly but is called
                *after* the class is fully initialized.
            
pydantic/main.py