[docs] [issue23987] docs about containers membership testing wrong for broken objects

[Jonathan Sharpe]

Changes by Jonathan Sharpe <j.r.sharpe+python at gmail.com>:


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assignee:  -> docs at python
components: +Documentation
nosy: +docs at python, jonrsharpe

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Python tracker <report at bugs.python.org>
<http://bugs.python.org/issue23987>
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