The code in Listing 2.9 may look rather mysterious—we’ll cover validations more thoroughly starting in Section 6.2—but its effects are readily apparent if we go to the

  new micropost page and enter more than 140 characters for the content of the post. As seen in Figure 2.14, Rails renders error messages indicating that the micropost’s content is too long. (We’ll learn more about error messages in Section 7.3.2.)