"Agile Web Development with Rails 5", p.76 lists a form partial which begins:
<%= form_for(product) do |f| %>
<% if product.errors.any? %>
<h2><%= pluralize(product.errors.count, "error") %> prohibited this product from being saved:</h2>
<% product.errors.full_messages.each do |message| %>
<li><%= message %></li>
It is correct but I'm confused about the first line as I understood that control structures begin with <% as in the 2nd line and that <%= is reserved for inserting values and calling formatting functions.