class ActionView::Helpers::FormBuilder

<% end %>
<%# =>
<%= f.field_tag :tag, name: f.field_name(:tag, multiple: true) %>
<%= form_for @post do |f| %>

<% end %>
<%# =>
<%= f.text_field :title, name: f.field_name(:title, :subtitle) %>
<%= form_for @post do |f| %>

attribute name.
Return the value generated by the FormBuilder for the given

field combination
Generate an HTML name attribute value for the given name and

def field_name(method, *methods, multiple: false, index: @options[:index])
  object_name = @options.fetch(:as) { @object_name }
  @template.field_name(object_name, method, *methods, index: index, multiple: multiple)
end