What is 'The DOM'?
You can see a nice representation of the current DOM in the Chrome Debugger's element inspector.
This code searches the DOM (what you see inside element inspector) for all elements which have the
"red" css class applied.
<p class="red">Red Text</p>
If you had a
<p class="red"> like the one above, then
document.querySelectorAll(".red") would return it as part of a list of matching elements.
If you're running Node (not a browser) there is no DOM, because there is no HTML being rendered! The function mentioned above doesn't exist inside Node.
We have this section because it's a nice milestone you can achieve quickly!
If you'd like to skip - that's fine, you should continue to the Modern Interactive Websites section.
However, I recommend continuing, we're going to go fast, and not too deep, since it's just a step on your way to Modern Interactive Website greatness and you'll also learn some useful things about the DOM along the way.