class SimpleForm::Inputs::BooleanInput

def boolean_label_class 

def boolean_label_class
  options[:boolean_label_class] || SimpleForm.boolean_label_class
end

def build_check_box(unchecked_value, options)

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, options)
  @builder.check_box(attribute_name, options, checked_value, unchecked_value)
end

def build_check_box_without_hidden_field(options)

#build_hidden_field_for_checkbox for more info.
Build a checkbox without generating the hidden field. See 
def build_check_box_without_hidden_field(options)
  build_check_box(nil, options)
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
  return "".html_safe if !include_hidden? || !unchecked_value
  options = { value: unchecked_value, id: nil, disabled: input_html_options[:disabled] }
  options[:name] = input_html_options[:name] if input_html_options.key?(:name)
  options[:form] = input_html_options[:form] if input_html_options.key?(:form)
  @builder.hidden_field(attribute_name, options)
end

def checked_value 

def checked_value
  options.fetch(:checked_value, '1')
end

def include_hidden? 

def include_hidden?
  options.fetch(:include_hidden, true)
end

def inline_label 

def inline_label
  inline_option = options[:inline_label]
  if inline_option
    label = inline_option == true ? label_text : html_escape(inline_option)
    " #{label}".html_safe
  end
end

def inline_label? 

def inline_label?
  nested_boolean_style? && options[:inline_label]
end

def input(wrapper_options = nil) 

def input(wrapper_options = nil)
  merged_input_options = merge_wrapper_options(input_html_options, wrapper_options)
  if nested_boolean_style?
    build_hidden_field_for_checkbox +
      template.label_tag(nil, class: boolean_label_class) {
        build_check_box_without_hidden_field(merged_input_options) +
          inline_label
      }
  else
    if include_hidden?
      build_check_box(unchecked_value, merged_input_options)
    else
      build_check_box_without_hidden_field(merged_input_options)
    end
  end
end

def label_input(wrapper_options = nil) 

def label_input(wrapper_options = nil)
  if options[:label] == false || inline_label?
    input(wrapper_options)
  elsif nested_boolean_style?
    html_options = label_html_options.dup
    html_options[:class] ||= []
    html_options[:class].push(boolean_label_class) if boolean_label_class
    merged_input_options = merge_wrapper_options(input_html_options, wrapper_options)
    build_hidden_field_for_checkbox +
      @builder.label(label_target, html_options) {
        build_check_box_without_hidden_field(merged_input_options) + label_text
      }
  else
    input(wrapper_options) + label(wrapper_options)
  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

def unchecked_value 

def unchecked_value
  options.fetch(:unchecked_value, '0')
end