BlockValidator is a special EachValidator which receives a block on initialization and call this block for each attribute being validated. validates_each uses this validator.

Methods
N
Class Public methods
new(options, &block)

Source: show | on GitHub 

     # File activemodel/lib/active_model/validator.rb, line 173
173:     def initialize(options, &block)
174:       @block = block
175:       super
176:     end