Just like with other programming languages such as Python, it is often helpful to include comments in your code. Comments don't display to the end user on the web page, but are just for the programmer to see (or anyone else looking at the code). They are like little reminders to yourself as you're building the page, reminding you of what you are trying to do (or sometimes what you still need to do). They also are very helpful when others might need to modify your code later.
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You don't have to include comments, but it can be very helpful to you - and to other coders you might be working with.