Submit button text comes from where (Ruby on rails)?

Question

I'm using the ruby on rails guide here http://guides.rubyonrails.org/getting_started.html

In section 5.13: I am getting two different text values displayed on the submit button, but in the "_form" partial file, the code is exactly the same. Rails seems to automatically change the text values somehow. Where is the code that is making this happen in the two views: new.html.erb and edit.html.erb.

(My question to control the text manually, but rather, I'm trying to understand where this automatic behavior is coming from in Rails. )

_partial

<%= form_for @post do |f| %>
<% if @post.errors.any? %>
<div id="error_explanation">
<h2><%= pluralize(@post.errors.count, "error") %> prohibited
  this post from being saved:</h2>
<ul>
<% @post.errors.full_messages.each do |msg| %>
  <li><%= msg %></li>
<% end %>
</ul>
</div>
 <% end %>
 <p>
  <%= f.label :title %><br>
<%= f.text_field :title %>
</p>

<p>
 <%= f.label :text %><br>
 <%= f.text_area :text %>
</p>

<p>
  <%= f.submit %>
</p>
<% end %>

posts_controller

    class PostsController < ApplicationController

def new
    @posts = Post.all
    @post = Post.new
end

def show
    @post = Post.find(params[:id])      
end

def index
    @posts = Post.all
end

# called by the posts_path function
def create
    @post = Post.new(post_params)
    if @post.save
        # Using redirect_to creates a new request.
        redirect_to @post
    else
        # Using render sends back the @post variable's data!
        # i.e. uses same request.
        render 'new'
    end
end

# Can only have one instance of render of redirect_to.
#render text: params[:post].inspect
def update
    @post = Post.find(params[:id])

    if @post.update(params[:post].permit(:title, :text))
        redirect_to @post
    else
        render 'edit'
    end
end

def edit
    @post = Post.find(params[:id])
end

# For SQL injection prevention.
private
    def post_params
        params.require(:post).permit(:title, :text)
    end

end

new.html.erb

New Post

      <%= form_for :post, url: posts_path do |f| %> 
<% if @post.errors.any? %>
    <div id="error_explanation">
      <h2><%= pluralize(@post.errors.count, "error") %> prohibited
        this post from being saved:</h2>
      <ul>
            <% @post.errors.full_messages.each do |msg| %>
  <li><%= msg %></li>
            <% end %>
      </ul>
    </div>
    <% end %>

<p>
    <%= f.label :title %><br>
    <%= f.text_field :title %>
</p>

<p>
    <%= f.label :text %><br>
    <%= f.text_area :text %>
</p>

<p>
    <%= f.submit %>
</p>
  <% end %>

  <%= form_for :post do|f| %>

  <% end %>

  <%= link_to "List of Posts", posts_path %>

edit.html.erb

Edit post

  <%= render 'form' %>

  <%= link_to 'Back', posts_path %>

Answer 1

if you want to change text at form's submit button:

<%= f.submit ( f.object.new_record? ? "Create" : "Update"), class: "btn" %>