This perk adds a new field setting for fields that support the placeholder property. More on that below. After you’ve specified the placeholder for a field, the Placeholder perk handles updating the field’s input HTML to include the placeholder attribute. For browsers that support placeholders (like Firefox, Chrome and Safari), this functionality will work natively. That means no special scripts!
But alas, not all browsers support placeholders just yet. For these browsers (like Internet Explorer), the Placeholder perk loads a little jQuery Placeholder script by Daniel Stocks. This script adds support for the placeholder attribute to older browsers so regardless of the browser, the user receives a uniform experience.