This is optional reading. In this target we'll link you to external documentation that you can look at if you want to. Do that only if you are curious and have the time to spare. Otherwise you can safely skip this chapter.
Here are a few references for the HTML specifications and documentations. These contain details about all the HTML elements and the places they can be used within our web pages.
Here are a few tutorials that can help you with understanding HTML based web page development in detail.