[Rails] formats in action view base

When you invoke ActionView::Base, it in turn invokes a LookupContext
object. The LookupContext class object has some class level macros
that builds some instance methods corresponding to a format:




register_detail(:formats) { ActionView::Base.default_formats ||
[:html, :text, :js, :css, :xml, :json] }
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


So these methods are included as instance methods via the Accessors
module. Later the LookupContext class override the formats method with
its own definition:

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

1) So what was the purpose of adding a formats method to the Accessors
module and then include it into LookupContext, if it will always be
overriden by LookupContext's own implementation?

2) What is meant by expand ["*/*"] values in the comment "# Override
formats= to expand ["*/*"] values " which is directly above the
formats implementation on LookupContext?

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