Sometimes, you don't want the user to leave the page. Ideally, this is when leaving the page would cause content to be lost, like a half-filled form, and not becacuse you're running a spam site.
useBlock hook will trigger a user confirmation that requires user input before navigation will occur.
Use the three buttons at the top of the Sandbox to toggle view modes. Clicking the menu button in the top left corner opens a menu to switch between files.