They don’t always know what an element’s default properties are. Languages outside the realm of the Web platform, like XUL through the XULElement interface, also implement Element. Content is available under these licenses. The MDN HTML Elements Reference has been indispensable while teaching my students - but there is one area that causes them the most confusion. Ensure that you have declared a div element in which the map will appear on the screen. HTML Reference is free and always will be!