email validator disallowing double dots.
secure password for test set to minimum cost.
gravartar feture: helper methods locate on app/helpers/NAME_helper.rb
css work for beautify profile.
signup form. see 7.2 more.
7.3.2 strong parameters implementation.
7.3.3 Signup for error messages: form validation.
7.4.1 successful signup redirection.
7.4.2 the flash.
SSL for production.