<% #TODO: generar distintas vistas en new y edit  %>
<%= simple_form_for  [:backend, resource] do |f| %>
  <%= f.input :numero, :label =>"Numero" %>
  <%= f.input :autor %>
  <%= f.simple_fields_for :pases do |pases_form| %>
    <%= pases_form.input :area %>
    <%= pases_form.input :ingreso, as: :datepicker %>
    <%= pases_form.input :fojas %>
  <% end %>
  <%= f.input :tags_tokens,
    :input_html => {
      "data-pre" => f.object.tags.to_json(:methods => :name), :only => [:id, :name] } %>
<%= f.submit %>
<% end %>

<% #TODO: generar distintas vistas en new y edit  %>
<% #TODO: Arreglar los datepicker que estan de mas  %>
<%= simple_form_for  [:backend, resource] do |f| %>
  <%= f.input :numero, :label =>"Numero" %>
  <%= f.input :autor %>
  <%= f.simple_fields_for :pases do |pases_form| %>
    <%= pases_form.association :area %>
    <%= pases_form.input :ingreso, as: :datepicker %>
    <%= pases_form.input :fojas %>
  <% end %>
  <%= f.association :tags, input_html: {multiple: true, class: 'chzn-select',
      "data-pre"  => f.object.tags.to_json(methods: :name), only: [:id, :name]} %>
<%= f.submit %>
<% end %>

Add a TODO, Area and Tags are now associations (instead of inputs) so simple form displays ok. Add chzn-select class in order to get the chosen plugin working correctly.
Add a TODO, Area and Tags are now associations (instead of inputs) so simple form displays ok. 
Add chzn-select class in order to get the chosen plugin working correctly.