FormHelpers and validation

1. from_for code: (form_tag_helper.rb):

module FormHelper

def form_for(object_name, object, options={}, &block)
  concat('<form ... >')
  fields_for(object_name,object,options,&block)
  concat('</form>')
end

def fields_for(object_name,object,options={}, &block)
  yield builder.new(object_name,object,self,options,block)
end

def text_field(object_name, method, options = {})
  InstanceTag.new(object_name, method, self, nil, options.delete(:object)).to_input_field_tag("text", options)
end

end

class FormBuilder
  def initialize(object_name, object, template, options, proc)
    @object_name, @object, @template, @options, @proc = object_name, object, template, options, proc        
  end
  ...
  def text_field(method,options)
     @template.text_field(@object_name,method,options.merge(:object => @object))
  end
  ...
  def fields_for(name, *args, &block)
    name = "#{object_name}[#{name}]"
    @template.fields_for(name, *args, &block)
  end
end

  def tag(name, options = nil, open = false, escape = true)
    "<#{name}#{tag_options(options, escape) if options}" + (open ? ">" : " />")
  end
  
  def tag(name, options)
    if object.respond_to?("errors") && object.errors.respond_to?("on")
      error_wrapping(tag_without_error_wrapping(name, options), object.errors.on(@method_name))
    else
       super
    end
  end

  def tag_options(options, escape = true)
    unless options.blank?
    attrs = []
    if escape
      options.each do |key, value|
        next unless value
        key = key.to_s
        value = BOOLEAN_ATTRIBUTES.include?(key) ? key : escape_once(value)
        attrs << %(#{key}="#{value}")
      end
    else
      attrs = options.map { |key, value| %(#{key}="#{value}") }
    end
    " #{attrs.sort * ' '}" unless attrs.empty?
  end
end
  

Tag helper is:

class InstanceTag 
      def initialize(object_name, method_name, template_object, local_binding = nil, object = nil)
        @object_name, @method_name = object_name.to_s.dup, method_name.to_s.dup
        @template_object, @local_binding = template_object, local_binding
        @object = object
        if @object_name.sub!(/\[\]$/,"")
          if object ||= @template_object.instance_variable_get("@#{Regexp.last_match.pre_match}") and object.respond_to?(:id_before_type_cast)
            @auto_index = object.id_before_type_cast
          else
            raise ArgumentError, "object[] naming but object param and @object var don't exist or don't respond to id_before_type_cast: #{object.inspect}"
          end
        end
      end

      def to_input_field_tag(field_type, options = {})
        options = options.stringify_keys
        options["size"] = options["maxlength"] || DEFAULT_FIELD_OPTIONS["size"] unless options.key?("size")
        options = DEFAULT_FIELD_OPTIONS.merge(options)
        if field_type == "hidden"
          options.delete("size")
        end
        options["type"] = field_type
        options["value"] ||= value_before_type_cast(object) unless field_type == "file"
        add_default_name_and_id(options)
        tag("input", options)
      end

end