class ActionView::Helpers::DateTimeSelector

def month_name(number)

depending on the format string.

month_name(1) # => "January (01)"

If the :month_format_string option is passed:

month_name(1) # => "1 - January"

If the :add_month_numbers option is passed:

month_name(1) # => '01'

If the :use_two_month_numbers option is passed:

month_name(1) # => 1

If the :use_month_numbers option is passed:

month_name(1) # => "January"

Looks up month names by number (1-based): 
def month_name(number)
  if @options[:use_month_numbers]
    number
  elsif @options[:use_two_digit_numbers]
    "%02d" % number
  elsif @options[:add_month_numbers]
    "#{number} - #{month_names[number]}"
  elsif format_string = @options[:month_format_string]
    format_string % { number: number, name: month_names[number] }
  else
    month_names[number]
  end
end