I can't understand the essence of the comment tag<!-- -->since it shows nothing when I RUN it .

Answer 1

Stanley Omus
Writing comments is helpful and it's a good practice to follow when writing source code. Comments help you document and communicate about your code and thought process to yourself (and others). It also reminds you what you were thinking/doing when you come back to a project after months of not working on it.

Comments also help you communicate with other developers who are working on the project with you. Your comments can clearly explain to them why you added certain lines of code.