class ActionView::LookupContext

:nodoc:
this key is generated just once during the request, it speeds up all cache accesses.
generate a key, given to view paths, used in the resolver cache lookup. Since
templates, i.e. view paths and details. The LookupContext is also responsible to
LookupContext is the object responsible to hold all information required to lookup
= Action View Lookup Context

def self.register_detail(name, options = {}, &block) 

def self.register_detail(name, options = {}, &block)
  self.registered_details << name
  initialize = registered_details.map { |n| "@details[:#{n}] = details[:#{n}] || default_#{n}" }
  Accessors.send :define_method, :"default_#{name}", &block
  Accessors.module_eval <<-METHOD, __FILE__, __LINE__ + 1
    def #{name}
      @details.fetch(:#{name}, [])
    end
    def #{name}=(value)
      value = value.present? ? Array(value) : default_#{name}
      _set_detail(:#{name}, value) if value != @details[:#{name}]
    end
    remove_possible_method :initialize_details
    def initialize_details(details)
      #{initialize.join("\n")}
    end
  METHOD
end

def formats=(values)

add :html as fallback to :js.
Override formats= to expand ["*/*"] values and automatically 
def formats=(values)
  if values
    values.concat(default_formats) if values.delete "*/*"
    if values == [:js]
      values << :html
      @html_fallback_for_js = true
    end
  end
  super(values)
end

def initialize(view_paths, details = {}, prefixes = []) 

def initialize(view_paths, details = {}, prefixes = [])
  @details, @details_key = {}, nil
  @skip_default_locale = false
  @cache = true
  @prefixes = prefixes
  @rendered_format = nil
  self.view_paths = view_paths
  initialize_details(details)
end

def locale

Override locale to return a symbol instead of array. 
def locale
  @details[:locale].first
end

def locale=(value)

acting as proxy, which we need to skip.
to original_config, it means that it has a copy of the original I18n configuration and it's
Overload locale= to also set the I18n.locale. If the current I18n.config object responds 
def locale=(value)
  if value
    config = I18n.config.respond_to?(:original_config) ? I18n.config.original_config : I18n.config
    config.locale = value
  end
  super(@skip_default_locale ? I18n.locale : default_locale)
end

def skip_default_locale!

Do not use the default locale on template lookup. 
def skip_default_locale!
  @skip_default_locale = true
  self.locale = nil
end

def with_layout_format

Uses the first format in the formats array for layout lookup. 
def with_layout_format
  if formats.size == 1
    yield
  else
    old_formats = formats
    _set_detail(:formats, formats[0,1])
    begin
      yield
    ensure
      _set_detail(:formats, old_formats)
    end
  end
end