class SimpleForm::Inputs::BooleanInput

def build_check_box(unchecked_value='0')

in Rails > 3.2.1, and is backported in SimpleForm AV helpers.
which won't generate the hidden checkbox. This is the default functionality
reuse the method for nested boolean style, but with no unchecked value,
Build a checkbox tag using default unchecked value. This allows us to 
def build_check_box(unchecked_value='0')
  @builder.check_box(attribute_name, input_html_options, '1', unchecked_value)
end

def build_check_box_without_hidden_field

#build_hidden_field_for_checkbox for more info.
Build a checkbox without generating the hidden field. See 
def build_check_box_without_hidden_field
  build_check_box(nil)
end

def build_hidden_field_for_checkbox

generates invalid html - html5 only).
we need the hidden field to be *outside* the label (otherwise it
functionality with hidden + checkbox, but under a nested context, where
Create a hidden field for the current checkbox, so we can simulate Rails 
def build_hidden_field_for_checkbox
  @builder.hidden_field(attribute_name, :value => '0', :id => nil,
                        :disabled => input_html_options[:disabled])
end

def input 

def input
  if nested_boolean_style?
    build_hidden_field_for_checkbox +
      template.label_tag(nil, :class => "checkbox") {
        build_check_box_without_hidden_field
      }
  else
    build_check_box
  end
end

def label_input 

def label_input
  if options[:label] == false
    input
  elsif nested_boolean_style?
    html_options = label_html_options.dup
    html_options[:class].push(:checkbox)
    build_hidden_field_for_checkbox +
      @builder.label(label_target, html_options) {
        build_check_box_without_hidden_field + label_text
      }
  else
    input + label
  end
end

def required_by_default?

Terms of Use usually presented at most sites sign up screen.
it makes no sense marking them as required. The only exception is
Booleans are not required by default because in most of the cases 
def required_by_default?
  false
end