Similar to the previous recipe, this plugin uses the add_filter function to register a custom function to be called by WordPress as it prepares an item's content to be displayed on the screen. When the filter function is called, the first action that it performs is to create a URL to the email icon that was downloaded in the recipe. It then goes on to modify the original content by appending the HTML code to display a mailto link. The same technique could be used to create links to popular social media and link sharing sites, with simple changes to the syntax of the link. Once the new content is ready, it is returned back to WordPress to be sent to any other registered filters and subsequently be displayed on the site.