form_error_field(:user, :name)
# if flash[:errors] contains {:name => "Please input a valid name"} OR if flash[:errors] contains "Please input a valid name":
# => <label for="user_name">Please input a valid name</label>

form_error_field(:user, :name, { :class => "alert-danger"})
# if flash[:errors] contains {:name => "Please input a valid name"} OR if flash[:errors] contains "Please input a valid name":
# => <label class="alert-danger" for="user_name">Please input a valid name</label>

form_error_field(:user, :email, { style: "color:red;"}, :err_msg)
# if flash[:err_msg] contains {:email => "Please input a valid email"} OR if flash[:err_msg] contains "Please input a valid email":
# => <label style="color:red;" for="user_email">Please input a valid email</label>