In the div tag, the hero-unit CSS class has a special meaning to Bootstrap, as do the btn, btn-large, and btn-primary classes in the signup button.
               The second link_to shows off the image_tag helper, which takes as arguments the path to an image and an optional options hash, in this case setting the alt attribute of the image tag using symbols. To make this clearer, let’s look at the HTML this tag produces:4

The alt attribute is what will be displayed if there is no image, and it is also what will be displayed by screen readers for the visually impaired. Although people are sometimes sloppy about including the alt attribute for images, it is in fact required by the HTML standard. Luckily, Rails includes a default alt attribute; if you don’t specify the attribute in the call to image_tag, Rails just uses the image filename (minus extension). In this case, though, we’ve set the alt text explicitly in order to capitalize ‘‘Rails.’’

                    Now we’re finally ready to see the fruits of our labors (Figure 5.2). Pretty underwhelming, you say? Perhaps so. Happily, though, we’ve done a good job of giving our HTML elements sensible classes, which puts us in a great position to add style to the site with CSS.

By the way, you might be surprised to discover that the rails.png image actually exists. Where did it come from? It’s included for free with every new Rails application, and you will find it in app/assets/images/rails.png. Because we used the image_tag helper, Rails finds it automatically using the asset pipeline (Section 5.2)