Ctrl-L is usually a shortcut to get the focus to the URL bar of my browser. I use it all the time when I want to navigate away from a site by giving a URL or a search term.
Unfortunately, the playpen decides to capture this shortcut and shows a "Go to line" dialogue. Given the fact that the playpen is not an IDE, I doubt the usefulness of this feature -- and I definitely think that this feature is not important enough to overwrite standard browser shortcuts.