how to set a line as comment in html code example

Example 1: how to comment out html

<!-- a comment in html -->

Example 2: 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.