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This release significantly tightens validation in :class:`hypothesis.settings`.
:obj:`~hypothesis.settings.max_examples`, ``buffer_size``,
and :obj:`~hypothesis.settings.stateful_step_count` must be positive integers;
:obj:`~hypothesis.settings.deadline` must be a positive number or ``None``; and
:obj:`~hypothesis.settings.derandomize` must be either ``True`` or ``False``.
As usual, this replaces existing errors with a more helpful error and starts new
validation checks as deprecation warnings.