ActionView::Helpers::InstanceTag#to_date_tag help

I'm trying to read through the code, hoping to find a way to custom style select boxes for a date_select and can't figure out this code. Any help appreciated:

<code>       def to_date_tag()         defaults = DEFAULT_DATE_OPTIONS.dup         date = value(object) ||         options = { |position| defaults.merge(:prefix => "#{@object_name}[#{@method_name}(#{position}i)]") }         html_day_select(date, +         html_month_select(date, +         html_year_select(date,       end </code>

Specifically, where are html_day_select, html_month_select, and html_year_select defined? Is there a method_missing definition that I'm not finding that's handling these calls?