module Roda::RodaPlugins::Mailer::InstanceMethods

def _mail_part(meth, body, headers=nil)

using the given body and optional headers.
Set the text_part or html_part (depending on the method) in the related email,
def _mail_part(meth, body, headers=nil)
  env['roda.mail'].public_send(meth) do
    body(body)
    headers(headers) if headers
  end
  nil
end