MDN supports displaying code blocks within the articles as live samples, enabling readers to see both the code and its output as it would look on a web page. This feature allows readers to understand exactly what the executed code would produce, making the documentation dynamic and instructive.
It also allows authors to be absolutely sure that the code blocks in documentation have the expected output, and work appropriately when used with different browsers....be in a code block, with a separate block for each language, properly...For clarity this example separates the logging code and the code...