how to add a note to element in html code example

Example 1: how to create comments in html5

Insert a single-line, or multi-line comment. 
Comments are designated by the tags <! -- and -->

Use the comment function to hide scripts on unsupported browsers
. If you are programming in JavaScript or VBScript, 
you can use the comment function to hide the script on browsers 
that don't support it. Insert the comment at the start of the 
script, and end it with //--> to ensure that the script works 
on browsers that do support it.

Example 2: html comment

<!--HTML Comment Example! HTML Comments do not affect your code in
any way, comments can be used to take notes to yourself, or if you 
are working with a team, this could be a good way to communicate 
without messing up any of your code. Comments will not be shown 
in your HTML webpage. -->