Okay, I'm gonna pause committing for a bit and review the sentence here first.

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If set to true and the current rule does not validate, the current validation error message is then returned and all following rules for the current field will not be checked. 

Practically, one should always use 'last' => true here since there is only one rule to be validated. For more relevant usages, see :doc:#multiple-rules-per-field

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When you say it doesn't make sense for 1.x, why? I still see the relevance in 1.x in multiple rules per field.